diff --git a/CODING_STYLE b/CODING_STYLE deleted file mode 100644 index cb8edcbb36..0000000000 --- a/CODING_STYLE +++ /dev/null @@ -1,216 +0,0 @@ -QEMU Coding Style -================= - -Please use the script checkpatch.pl in the scripts directory to check -patches before submitting. - -1. Whitespace - -Of course, the most important aspect in any coding style is whitespace. -Crusty old coders who have trouble spotting the glasses on their noses -can tell the difference between a tab and eight spaces from a distance -of approximately fifteen parsecs. Many a flamewar has been fought and -lost on this issue. - -QEMU indents are four spaces. Tabs are never used, except in Makefiles -where they have been irreversibly coded into the syntax. -Spaces of course are superior to tabs because: - - - You have just one way to specify whitespace, not two. Ambiguity breeds - mistakes. - - The confusion surrounding 'use tabs to indent, spaces to justify' is gone. - - Tab indents push your code to the right, making your screen seriously - unbalanced. - - Tabs will be rendered incorrectly on editors who are misconfigured not - to use tab stops of eight positions. - - Tabs are rendered badly in patches, causing off-by-one errors in almost - every line. - - It is the QEMU coding style. - -Do not leave whitespace dangling off the ends of lines. - -1.1 Multiline Indent - -There are several places where indent is necessary: - - - if/else - - while/for - - function definition & call - -When breaking up a long line to fit within line width, we need a proper indent -for the following lines. - -In case of if/else, while/for, align the secondary lines just after the -opening parenthesis of the first. - -For example: - - if (a == 1 && - b == 2) { - - while (a == 1 && - b == 2) { - -In case of function, there are several variants: - - * 4 spaces indent from the beginning - * align the secondary lines just after the opening parenthesis of the - first - -For example: - - do_something(x, y, - z); - - do_something(x, y, - z); - - do_something(x, do_another(y, - z)); - -2. Line width - -Lines should be 80 characters; try not to make them longer. - -Sometimes it is hard to do, especially when dealing with QEMU subsystems -that use long function or symbol names. Even in that case, do not make -lines much longer than 80 characters. - -Rationale: - - Some people like to tile their 24" screens with a 6x4 matrix of 80x24 - xterms and use vi in all of them. The best way to punish them is to - let them keep doing it. - - Code and especially patches is much more readable if limited to a sane - line length. Eighty is traditional. - - The four-space indentation makes the most common excuse ("But look - at all that white space on the left!") moot. - - It is the QEMU coding style. - -3. Naming - -Variables are lower_case_with_underscores; easy to type and read. Structured -type names are in CamelCase; harder to type but standing out. Enum type -names and function type names should also be in CamelCase. Scalar type -names are lower_case_with_underscores_ending_with_a_t, like the POSIX -uint64_t and family. Note that this last convention contradicts POSIX -and is therefore likely to be changed. - -When wrapping standard library functions, use the prefix qemu_ to alert -readers that they are seeing a wrapped version; otherwise avoid this prefix. - -4. Block structure - -Every indented statement is braced; even if the block contains just one -statement. The opening brace is on the line that contains the control -flow statement that introduces the new block; the closing brace is on the -same line as the else keyword, or on a line by itself if there is no else -keyword. Example: - - if (a == 5) { - printf("a was 5.\n"); - } else if (a == 6) { - printf("a was 6.\n"); - } else { - printf("a was something else entirely.\n"); - } - -Note that 'else if' is considered a single statement; otherwise a long if/ -else if/else if/.../else sequence would need an indent for every else -statement. - -An exception is the opening brace for a function; for reasons of tradition -and clarity it comes on a line by itself: - - void a_function(void) - { - do_something(); - } - -Rationale: a consistent (except for functions...) bracing style reduces -ambiguity and avoids needless churn when lines are added or removed. -Furthermore, it is the QEMU coding style. - -5. Declarations - -Mixed declarations (interleaving statements and declarations within -blocks) are generally not allowed; declarations should be at the beginning -of blocks. - -Every now and then, an exception is made for declarations inside a -#ifdef or #ifndef block: if the code looks nicer, such declarations can -be placed at the top of the block even if there are statements above. -On the other hand, however, it's often best to move that #ifdef/#ifndef -block to a separate function altogether. - -6. Conditional statements - -When comparing a variable for (in)equality with a constant, list the -constant on the right, as in: - - if (a == 1) { - /* Reads like: "If a equals 1" */ - do_something(); - } - -Rationale: Yoda conditions (as in 'if (1 == a)') are awkward to read. -Besides, good compilers already warn users when '==' is mis-typed as '=', -even when the constant is on the right. - -7. Comment style - -We use traditional C-style /* */ comments and avoid // comments. - -Rationale: The // form is valid in C99, so this is purely a matter of -consistency of style. The checkpatch script will warn you about this. - -Multiline comment blocks should have a row of stars on the left, -and the initial /* and terminating */ both on their own lines: - /* - * like - * this - */ -This is the same format required by the Linux kernel coding style. - -(Some of the existing comments in the codebase use the GNU Coding -Standards form which does not have stars on the left, or other -variations; avoid these when writing new comments, but don't worry -about converting to the preferred form unless you're editing that -comment anyway.) - -Rationale: Consistency, and ease of visually picking out a multiline -comment from the surrounding code. - -8. trace-events style - -8.1 0x prefix - -In trace-events files, use a '0x' prefix to specify hex numbers, as in: - -some_trace(unsigned x, uint64_t y) "x 0x%x y 0x" PRIx64 - -An exception is made for groups of numbers that are hexadecimal by -convention and separated by the symbols '.', '/', ':', or ' ' (such as -PCI bus id): - -another_trace(int cssid, int ssid, int dev_num) "bus id: %x.%x.%04x" - -However, you can use '0x' for such groups if you want. Anyway, be sure that -it is obvious that numbers are in hex, ex.: - -data_dump(uint8_t c1, uint8_t c2, uint8_t c3) "bytes (in hex): %02x %02x %02x" - -Rationale: hex numbers are hard to read in logs when there is no 0x prefix, -especially when (occasionally) the representation doesn't contain any letters -and especially in one line with other decimal numbers. Number groups are allowed -to not use '0x' because for some things notations like %x.%x.%x are used not -only in Qemu. Also dumping raw data bytes with '0x' is less readable. - -8.2 '#' printf flag - -Do not use printf flag '#', like '%#x'. - -Rationale: there are two ways to add a '0x' prefix to printed number: '0x%...' -and '%#...'. For consistency the only one way should be used. Arguments for -'0x%' are: - - it is more popular - - '%#' omits the 0x for the value 0 which makes output inconsistent diff --git a/CODING_STYLE.rst b/CODING_STYLE.rst new file mode 100644 index 0000000000..427699e0e4 --- /dev/null +++ b/CODING_STYLE.rst @@ -0,0 +1,641 @@ +================= +QEMU Coding Style +================= + +.. contents:: Table of Contents + +Please use the script checkpatch.pl in the scripts directory to check +patches before submitting. + +Formatting and style +******************** + +Whitespace +========== + +Of course, the most important aspect in any coding style is whitespace. +Crusty old coders who have trouble spotting the glasses on their noses +can tell the difference between a tab and eight spaces from a distance +of approximately fifteen parsecs. Many a flamewar has been fought and +lost on this issue. + +QEMU indents are four spaces. Tabs are never used, except in Makefiles +where they have been irreversibly coded into the syntax. +Spaces of course are superior to tabs because: + +* You have just one way to specify whitespace, not two. Ambiguity breeds + mistakes. +* The confusion surrounding 'use tabs to indent, spaces to justify' is gone. +* Tab indents push your code to the right, making your screen seriously + unbalanced. +* Tabs will be rendered incorrectly on editors who are misconfigured not + to use tab stops of eight positions. +* Tabs are rendered badly in patches, causing off-by-one errors in almost + every line. +* It is the QEMU coding style. + +Do not leave whitespace dangling off the ends of lines. + +Multiline Indent +---------------- + +There are several places where indent is necessary: + +* if/else +* while/for +* function definition & call + +When breaking up a long line to fit within line width, we need a proper indent +for the following lines. + +In case of if/else, while/for, align the secondary lines just after the +opening parenthesis of the first. + +For example: + +.. code-block:: c + + if (a == 1 && + b == 2) { + + while (a == 1 && + b == 2) { + +In case of function, there are several variants: + +* 4 spaces indent from the beginning +* align the secondary lines just after the opening parenthesis of the first + +For example: + +.. code-block:: c + + do_something(x, y, + z); + + do_something(x, y, + z); + + do_something(x, do_another(y, + z)); + +Line width +========== + +Lines should be 80 characters; try not to make them longer. + +Sometimes it is hard to do, especially when dealing with QEMU subsystems +that use long function or symbol names. Even in that case, do not make +lines much longer than 80 characters. + +Rationale: + +* Some people like to tile their 24" screens with a 6x4 matrix of 80x24 + xterms and use vi in all of them. The best way to punish them is to + let them keep doing it. +* Code and especially patches is much more readable if limited to a sane + line length. Eighty is traditional. +* The four-space indentation makes the most common excuse ("But look + at all that white space on the left!") moot. +* It is the QEMU coding style. + +Naming +====== + +Variables are lower_case_with_underscores; easy to type and read. Structured +type names are in CamelCase; harder to type but standing out. Enum type +names and function type names should also be in CamelCase. Scalar type +names are lower_case_with_underscores_ending_with_a_t, like the POSIX +uint64_t and family. Note that this last convention contradicts POSIX +and is therefore likely to be changed. + +When wrapping standard library functions, use the prefix ``qemu_`` to alert +readers that they are seeing a wrapped version; otherwise avoid this prefix. + +Block structure +=============== + +Every indented statement is braced; even if the block contains just one +statement. The opening brace is on the line that contains the control +flow statement that introduces the new block; the closing brace is on the +same line as the else keyword, or on a line by itself if there is no else +keyword. Example: + +.. code-block:: c + + if (a == 5) { + printf("a was 5.\n"); + } else if (a == 6) { + printf("a was 6.\n"); + } else { + printf("a was something else entirely.\n"); + } + +Note that 'else if' is considered a single statement; otherwise a long if/ +else if/else if/.../else sequence would need an indent for every else +statement. + +An exception is the opening brace for a function; for reasons of tradition +and clarity it comes on a line by itself: + +.. code-block:: c + + void a_function(void) + { + do_something(); + } + +Rationale: a consistent (except for functions...) bracing style reduces +ambiguity and avoids needless churn when lines are added or removed. +Furthermore, it is the QEMU coding style. + +Declarations +============ + +Mixed declarations (interleaving statements and declarations within +blocks) are generally not allowed; declarations should be at the beginning +of blocks. + +Every now and then, an exception is made for declarations inside a +#ifdef or #ifndef block: if the code looks nicer, such declarations can +be placed at the top of the block even if there are statements above. +On the other hand, however, it's often best to move that #ifdef/#ifndef +block to a separate function altogether. + +Conditional statements +====================== + +When comparing a variable for (in)equality with a constant, list the +constant on the right, as in: + +.. code-block:: c + + if (a == 1) { + /* Reads like: "If a equals 1" */ + do_something(); + } + +Rationale: Yoda conditions (as in 'if (1 == a)') are awkward to read. +Besides, good compilers already warn users when '==' is mis-typed as '=', +even when the constant is on the right. + +Comment style +============= + +We use traditional C-style /``*`` ``*``/ comments and avoid // comments. + +Rationale: The // form is valid in C99, so this is purely a matter of +consistency of style. The checkpatch script will warn you about this. + +Multiline comment blocks should have a row of stars on the left, +and the initial /``*`` and terminating ``*``/ both on their own lines: + +.. code-block:: c + + /* + * like + * this + */ + +This is the same format required by the Linux kernel coding style. + +(Some of the existing comments in the codebase use the GNU Coding +Standards form which does not have stars on the left, or other +variations; avoid these when writing new comments, but don't worry +about converting to the preferred form unless you're editing that +comment anyway.) + +Rationale: Consistency, and ease of visually picking out a multiline +comment from the surrounding code. + +Language usage +************** + +Preprocessor +============ + +Variadic macros +--------------- + +For variadic macros, stick with this C99-like syntax: + +.. code-block:: c + + #define DPRINTF(fmt, ...) \ + do { printf("IRQ: " fmt, ## __VA_ARGS__); } while (0) + +Include directives +------------------ + +Order include directives as follows: + +.. code-block:: c + + #include "qemu/osdep.h" /* Always first... */ + #include <...> /* then system headers... */ + #include "..." /* and finally QEMU headers. */ + +The "qemu/osdep.h" header contains preprocessor macros that affect the behavior +of core system headers like . It must be the first include so that +core system headers included by external libraries get the preprocessor macros +that QEMU depends on. + +Do not include "qemu/osdep.h" from header files since the .c file will have +already included it. + +C types +======= + +It should be common sense to use the right type, but we have collected +a few useful guidelines here. + +Scalars +------- + +If you're using "int" or "long", odds are good that there's a better type. +If a variable is counting something, it should be declared with an +unsigned type. + +If it's host memory-size related, size_t should be a good choice (use +ssize_t only if required). Guest RAM memory offsets must use ram_addr_t, +but only for RAM, it may not cover whole guest address space. + +If it's file-size related, use off_t. +If it's file-offset related (i.e., signed), use off_t. +If it's just counting small numbers use "unsigned int"; +(on all but oddball embedded systems, you can assume that that +type is at least four bytes wide). + +In the event that you require a specific width, use a standard type +like int32_t, uint32_t, uint64_t, etc. The specific types are +mandatory for VMState fields. + +Don't use Linux kernel internal types like u32, __u32 or __le32. + +Use hwaddr for guest physical addresses except pcibus_t +for PCI addresses. In addition, ram_addr_t is a QEMU internal address +space that maps guest RAM physical addresses into an intermediate +address space that can map to host virtual address spaces. Generally +speaking, the size of guest memory can always fit into ram_addr_t but +it would not be correct to store an actual guest physical address in a +ram_addr_t. + +For CPU virtual addresses there are several possible types. +vaddr is the best type to use to hold a CPU virtual address in +target-independent code. It is guaranteed to be large enough to hold a +virtual address for any target, and it does not change size from target +to target. It is always unsigned. +target_ulong is a type the size of a virtual address on the CPU; this means +it may be 32 or 64 bits depending on which target is being built. It should +therefore be used only in target-specific code, and in some +performance-critical built-per-target core code such as the TLB code. +There is also a signed version, target_long. +abi_ulong is for the ``*``-user targets, and represents a type the size of +'void ``*``' in that target's ABI. (This may not be the same as the size of a +full CPU virtual address in the case of target ABIs which use 32 bit pointers +on 64 bit CPUs, like sparc32plus.) Definitions of structures that must match +the target's ABI must use this type for anything that on the target is defined +to be an 'unsigned long' or a pointer type. +There is also a signed version, abi_long. + +Of course, take all of the above with a grain of salt. If you're about +to use some system interface that requires a type like size_t, pid_t or +off_t, use matching types for any corresponding variables. + +Also, if you try to use e.g., "unsigned int" as a type, and that +conflicts with the signedness of a related variable, sometimes +it's best just to use the *wrong* type, if "pulling the thread" +and fixing all related variables would be too invasive. + +Finally, while using descriptive types is important, be careful not to +go overboard. If whatever you're doing causes warnings, or requires +casts, then reconsider or ask for help. + +Pointers +-------- + +Ensure that all of your pointers are "const-correct". +Unless a pointer is used to modify the pointed-to storage, +give it the "const" attribute. That way, the reader knows +up-front that this is a read-only pointer. Perhaps more +importantly, if we're diligent about this, when you see a non-const +pointer, you're guaranteed that it is used to modify the storage +it points to, or it is aliased to another pointer that is. + +Typedefs +-------- + +Typedefs are used to eliminate the redundant 'struct' keyword, since type +names have a different style than other identifiers ("CamelCase" versus +"snake_case"). Each named struct type should have a CamelCase name and a +corresponding typedef. + +Since certain C compilers choke on duplicated typedefs, you should avoid +them and declare a typedef only in one header file. For common types, +you can use "include/qemu/typedefs.h" for example. However, as a matter +of convenience it is also perfectly fine to use forward struct +definitions instead of typedefs in headers and function prototypes; this +avoids problems with duplicated typedefs and reduces the need to include +headers from other headers. + +Reserved namespaces in C and POSIX +---------------------------------- + +Underscore capital, double underscore, and underscore 't' suffixes should be +avoided. + +Low level memory management +=========================== + +Use of the malloc/free/realloc/calloc/valloc/memalign/posix_memalign +APIs is not allowed in the QEMU codebase. Instead of these routines, +use the GLib memory allocation routines g_malloc/g_malloc0/g_new/ +g_new0/g_realloc/g_free or QEMU's qemu_memalign/qemu_blockalign/qemu_vfree +APIs. + +Please note that g_malloc will exit on allocation failure, so there +is no need to test for failure (as you would have to with malloc). +Calling g_malloc with a zero size is valid and will return NULL. + +Prefer g_new(T, n) instead of g_malloc(sizeof(T) ``*`` n) for the following +reasons: + +* It catches multiplication overflowing size_t; +* It returns T ``*`` instead of void ``*``, letting compiler catch more type errors. + +Declarations like + +.. code-block:: c + + T *v = g_malloc(sizeof(*v)) + +are acceptable, though. + +Memory allocated by qemu_memalign or qemu_blockalign must be freed with +qemu_vfree, since breaking this will cause problems on Win32. + +String manipulation +=================== + +Do not use the strncpy function. As mentioned in the man page, it does *not* +guarantee a NULL-terminated buffer, which makes it extremely dangerous to use. +It also zeros trailing destination bytes out to the specified length. Instead, +use this similar function when possible, but note its different signature: + +.. code-block:: c + + void pstrcpy(char *dest, int dest_buf_size, const char *src) + +Don't use strcat because it can't check for buffer overflows, but: + +.. code-block:: c + + char *pstrcat(char *buf, int buf_size, const char *s) + +The same limitation exists with sprintf and vsprintf, so use snprintf and +vsnprintf. + +QEMU provides other useful string functions: + +.. code-block:: c + + int strstart(const char *str, const char *val, const char **ptr) + int stristart(const char *str, const char *val, const char **ptr) + int qemu_strnlen(const char *s, int max_len) + +There are also replacement character processing macros for isxyz and toxyz, +so instead of e.g. isalnum you should use qemu_isalnum. + +Because of the memory management rules, you must use g_strdup/g_strndup +instead of plain strdup/strndup. + +Printf-style functions +====================== + +Whenever you add a new printf-style function, i.e., one with a format +string argument and following "..." in its prototype, be sure to use +gcc's printf attribute directive in the prototype. + +This makes it so gcc's -Wformat and -Wformat-security options can do +their jobs and cross-check format strings with the number and types +of arguments. + +C standard, implementation defined and undefined behaviors +========================================================== + +C code in QEMU should be written to the C99 language specification. A copy +of the final version of the C99 standard with corrigenda TC1, TC2, and TC3 +included, formatted as a draft, can be downloaded from: + + ``_ + +The C language specification defines regions of undefined behavior and +implementation defined behavior (to give compiler authors enough leeway to +produce better code). In general, code in QEMU should follow the language +specification and avoid both undefined and implementation defined +constructs. ("It works fine on the gcc I tested it with" is not a valid +argument...) However there are a few areas where we allow ourselves to +assume certain behaviors because in practice all the platforms we care about +behave in the same way and writing strictly conformant code would be +painful. These are: + +* you may assume that integers are 2s complement representation +* you may assume that right shift of a signed integer duplicates + the sign bit (ie it is an arithmetic shift, not a logical shift) + +In addition, QEMU assumes that the compiler does not use the latitude +given in C99 and C11 to treat aspects of signed '<<' as undefined, as +documented in the GNU Compiler Collection manual starting at version 4.0. + +Automatic memory deallocation +============================= + +QEMU has a mandatory dependency either the GCC or CLang compiler. As +such it has the freedom to make use of a C language extension for +automatically running a cleanup function when a stack variable goes +out of scope. This can be used to simplify function cleanup paths, +often allowing many goto jumps to be eliminated, through automatic +free'ing of memory. + +The GLib2 library provides a number of functions/macros for enabling +automatic cleanup: + + ``_ + +Most notably: + +* g_autofree - will invoke g_free() on the variable going out of scope + +* g_autoptr - for structs / objects, will invoke the cleanup func created + by a previous use of G_DEFINE_AUTOPTR_CLEANUP_FUNC. This is + supported for most GLib data types and GObjects + +For example, instead of + +.. code-block:: c + + int somefunc(void) { + int ret = -1; + char *foo = g_strdup_printf("foo%", "wibble"); + GList *bar = ..... + + if (eek) { + goto cleanup; + } + + ret = 0; + + cleanup: + g_free(foo); + g_list_free(bar); + return ret; + } + +Using g_autofree/g_autoptr enables the code to be written as: + +.. code-block:: c + + int somefunc(void) { + g_autofree char *foo = g_strdup_printf("foo%", "wibble"); + g_autoptr (GList) bar = ..... + + if (eek) { + return -1; + } + + return 0; + } + +While this generally results in simpler, less leak-prone code, there +are still some caveats to beware of + +* Variables declared with g_auto* MUST always be initialized, + otherwise the cleanup function will use uninitialized stack memory + +* If a variable declared with g_auto* holds a value which must + live beyond the life of the function, that value must be saved + and the original variable NULL'd out. This can be simpler using + g_steal_pointer + + +.. code-block:: c + + char *somefunc(void) { + g_autofree char *foo = g_strdup_printf("foo%", "wibble"); + g_autoptr (GList) bar = ..... + + if (eek) { + return NULL; + } + + return g_steal_pointer(&foo); + } + + +QEMU Specific Idioms +******************** + +Error handling and reporting +============================ + +Reporting errors to the human user +---------------------------------- + +Do not use printf(), fprintf() or monitor_printf(). Instead, use +error_report() or error_vreport() from error-report.h. This ensures the +error is reported in the right place (current monitor or stderr), and in +a uniform format. + +Use error_printf() & friends to print additional information. + +error_report() prints the current location. In certain common cases +like command line parsing, the current location is tracked +automatically. To manipulate it manually, use the loc_``*``() from +error-report.h. + +Propagating errors +------------------ + +An error can't always be reported to the user right where it's detected, +but often needs to be propagated up the call chain to a place that can +handle it. This can be done in various ways. + +The most flexible one is Error objects. See error.h for usage +information. + +Use the simplest suitable method to communicate success / failure to +callers. Stick to common methods: non-negative on success / -1 on +error, non-negative / -errno, non-null / null, or Error objects. + +Example: when a function returns a non-null pointer on success, and it +can fail only in one way (as far as the caller is concerned), returning +null on failure is just fine, and certainly simpler and a lot easier on +the eyes than propagating an Error object through an Error ``*````*`` parameter. + +Example: when a function's callers need to report details on failure +only the function really knows, use Error ``*````*``, and set suitable errors. + +Do not report an error to the user when you're also returning an error +for somebody else to handle. Leave the reporting to the place that +consumes the error returned. + +Handling errors +--------------- + +Calling exit() is fine when handling configuration errors during +startup. It's problematic during normal operation. In particular, +monitor commands should never exit(). + +Do not call exit() or abort() to handle an error that can be triggered +by the guest (e.g., some unimplemented corner case in guest code +translation or device emulation). Guests should not be able to +terminate QEMU. + +Note that &error_fatal is just another way to exit(1), and &error_abort +is just another way to abort(). + + +trace-events style +================== + +0x prefix +--------- + +In trace-events files, use a '0x' prefix to specify hex numbers, as in: + +.. code-block:: + + some_trace(unsigned x, uint64_t y) "x 0x%x y 0x" PRIx64 + +An exception is made for groups of numbers that are hexadecimal by +convention and separated by the symbols '.', '/', ':', or ' ' (such as +PCI bus id): + +.. code-block:: + + another_trace(int cssid, int ssid, int dev_num) "bus id: %x.%x.%04x" + +However, you can use '0x' for such groups if you want. Anyway, be sure that +it is obvious that numbers are in hex, ex.: + +.. code-block:: + + data_dump(uint8_t c1, uint8_t c2, uint8_t c3) "bytes (in hex): %02x %02x %02x" + +Rationale: hex numbers are hard to read in logs when there is no 0x prefix, +especially when (occasionally) the representation doesn't contain any letters +and especially in one line with other decimal numbers. Number groups are allowed +to not use '0x' because for some things notations like %x.%x.%x are used not +only in Qemu. Also dumping raw data bytes with '0x' is less readable. + +'#' printf flag +--------------- + +Do not use printf flag '#', like '%#x'. + +Rationale: there are two ways to add a '0x' prefix to printed number: '0x%...' +and '%#...'. For consistency the only one way should be used. Arguments for +'0x%' are: + +* it is more popular +* '%#' omits the 0x for the value 0 which makes output inconsistent diff --git a/HACKING b/HACKING deleted file mode 100644 index 097d482603..0000000000 --- a/HACKING +++ /dev/null @@ -1,257 +0,0 @@ -1. Preprocessor - -1.1. Variadic macros - -For variadic macros, stick with this C99-like syntax: - -#define DPRINTF(fmt, ...) \ - do { printf("IRQ: " fmt, ## __VA_ARGS__); } while (0) - -1.2. Include directives - -Order include directives as follows: - -#include "qemu/osdep.h" /* Always first... */ -#include <...> /* then system headers... */ -#include "..." /* and finally QEMU headers. */ - -The "qemu/osdep.h" header contains preprocessor macros that affect the behavior -of core system headers like . It must be the first include so that -core system headers included by external libraries get the preprocessor macros -that QEMU depends on. - -Do not include "qemu/osdep.h" from header files since the .c file will have -already included it. - -2. C types - -It should be common sense to use the right type, but we have collected -a few useful guidelines here. - -2.1. Scalars - -If you're using "int" or "long", odds are good that there's a better type. -If a variable is counting something, it should be declared with an -unsigned type. - -If it's host memory-size related, size_t should be a good choice (use -ssize_t only if required). Guest RAM memory offsets must use ram_addr_t, -but only for RAM, it may not cover whole guest address space. - -If it's file-size related, use off_t. -If it's file-offset related (i.e., signed), use off_t. -If it's just counting small numbers use "unsigned int"; -(on all but oddball embedded systems, you can assume that that -type is at least four bytes wide). - -In the event that you require a specific width, use a standard type -like int32_t, uint32_t, uint64_t, etc. The specific types are -mandatory for VMState fields. - -Don't use Linux kernel internal types like u32, __u32 or __le32. - -Use hwaddr for guest physical addresses except pcibus_t -for PCI addresses. In addition, ram_addr_t is a QEMU internal address -space that maps guest RAM physical addresses into an intermediate -address space that can map to host virtual address spaces. Generally -speaking, the size of guest memory can always fit into ram_addr_t but -it would not be correct to store an actual guest physical address in a -ram_addr_t. - -For CPU virtual addresses there are several possible types. -vaddr is the best type to use to hold a CPU virtual address in -target-independent code. It is guaranteed to be large enough to hold a -virtual address for any target, and it does not change size from target -to target. It is always unsigned. -target_ulong is a type the size of a virtual address on the CPU; this means -it may be 32 or 64 bits depending on which target is being built. It should -therefore be used only in target-specific code, and in some -performance-critical built-per-target core code such as the TLB code. -There is also a signed version, target_long. -abi_ulong is for the *-user targets, and represents a type the size of -'void *' in that target's ABI. (This may not be the same as the size of a -full CPU virtual address in the case of target ABIs which use 32 bit pointers -on 64 bit CPUs, like sparc32plus.) Definitions of structures that must match -the target's ABI must use this type for anything that on the target is defined -to be an 'unsigned long' or a pointer type. -There is also a signed version, abi_long. - -Of course, take all of the above with a grain of salt. If you're about -to use some system interface that requires a type like size_t, pid_t or -off_t, use matching types for any corresponding variables. - -Also, if you try to use e.g., "unsigned int" as a type, and that -conflicts with the signedness of a related variable, sometimes -it's best just to use the *wrong* type, if "pulling the thread" -and fixing all related variables would be too invasive. - -Finally, while using descriptive types is important, be careful not to -go overboard. If whatever you're doing causes warnings, or requires -casts, then reconsider or ask for help. - -2.2. Pointers - -Ensure that all of your pointers are "const-correct". -Unless a pointer is used to modify the pointed-to storage, -give it the "const" attribute. That way, the reader knows -up-front that this is a read-only pointer. Perhaps more -importantly, if we're diligent about this, when you see a non-const -pointer, you're guaranteed that it is used to modify the storage -it points to, or it is aliased to another pointer that is. - -2.3. Typedefs - -Typedefs are used to eliminate the redundant 'struct' keyword, since type -names have a different style than other identifiers ("CamelCase" versus -"snake_case"). Each named struct type should have a CamelCase name and a -corresponding typedef. - -Since certain C compilers choke on duplicated typedefs, you should avoid -them and declare a typedef only in one header file. For common types, -you can use "include/qemu/typedefs.h" for example. However, as a matter -of convenience it is also perfectly fine to use forward struct -definitions instead of typedefs in headers and function prototypes; this -avoids problems with duplicated typedefs and reduces the need to include -headers from other headers. - -2.4. Reserved namespaces in C and POSIX -Underscore capital, double underscore, and underscore 't' suffixes should be -avoided. - -3. Low level memory management - -Use of the malloc/free/realloc/calloc/valloc/memalign/posix_memalign -APIs is not allowed in the QEMU codebase. Instead of these routines, -use the GLib memory allocation routines g_malloc/g_malloc0/g_new/ -g_new0/g_realloc/g_free or QEMU's qemu_memalign/qemu_blockalign/qemu_vfree -APIs. - -Please note that g_malloc will exit on allocation failure, so there -is no need to test for failure (as you would have to with malloc). -Calling g_malloc with a zero size is valid and will return NULL. - -Prefer g_new(T, n) instead of g_malloc(sizeof(T) * n) for the following -reasons: - - a. It catches multiplication overflowing size_t; - b. It returns T * instead of void *, letting compiler catch more type - errors. - -Declarations like T *v = g_malloc(sizeof(*v)) are acceptable, though. - -Memory allocated by qemu_memalign or qemu_blockalign must be freed with -qemu_vfree, since breaking this will cause problems on Win32. - -4. String manipulation - -Do not use the strncpy function. As mentioned in the man page, it does *not* -guarantee a NULL-terminated buffer, which makes it extremely dangerous to use. -It also zeros trailing destination bytes out to the specified length. Instead, -use this similar function when possible, but note its different signature: -void pstrcpy(char *dest, int dest_buf_size, const char *src) - -Don't use strcat because it can't check for buffer overflows, but: -char *pstrcat(char *buf, int buf_size, const char *s) - -The same limitation exists with sprintf and vsprintf, so use snprintf and -vsnprintf. - -QEMU provides other useful string functions: -int strstart(const char *str, const char *val, const char **ptr) -int stristart(const char *str, const char *val, const char **ptr) -int qemu_strnlen(const char *s, int max_len) - -There are also replacement character processing macros for isxyz and toxyz, -so instead of e.g. isalnum you should use qemu_isalnum. - -Because of the memory management rules, you must use g_strdup/g_strndup -instead of plain strdup/strndup. - -5. Printf-style functions - -Whenever you add a new printf-style function, i.e., one with a format -string argument and following "..." in its prototype, be sure to use -gcc's printf attribute directive in the prototype. - -This makes it so gcc's -Wformat and -Wformat-security options can do -their jobs and cross-check format strings with the number and types -of arguments. - -6. C standard, implementation defined and undefined behaviors - -C code in QEMU should be written to the C99 language specification. A copy -of the final version of the C99 standard with corrigenda TC1, TC2, and TC3 -included, formatted as a draft, can be downloaded from: - http://www.open-std.org/jtc1/sc22/WG14/www/docs/n1256.pdf - -The C language specification defines regions of undefined behavior and -implementation defined behavior (to give compiler authors enough leeway to -produce better code). In general, code in QEMU should follow the language -specification and avoid both undefined and implementation defined -constructs. ("It works fine on the gcc I tested it with" is not a valid -argument...) However there are a few areas where we allow ourselves to -assume certain behaviors because in practice all the platforms we care about -behave in the same way and writing strictly conformant code would be -painful. These are: - * you may assume that integers are 2s complement representation - * you may assume that right shift of a signed integer duplicates - the sign bit (ie it is an arithmetic shift, not a logical shift) - -In addition, QEMU assumes that the compiler does not use the latitude -given in C99 and C11 to treat aspects of signed '<<' as undefined, as -documented in the GNU Compiler Collection manual starting at version 4.0. - -7. Error handling and reporting - -7.1 Reporting errors to the human user - -Do not use printf(), fprintf() or monitor_printf(). Instead, use -error_report() or error_vreport() from error-report.h. This ensures the -error is reported in the right place (current monitor or stderr), and in -a uniform format. - -Use error_printf() & friends to print additional information. - -error_report() prints the current location. In certain common cases -like command line parsing, the current location is tracked -automatically. To manipulate it manually, use the loc_*() from -error-report.h. - -7.2 Propagating errors - -An error can't always be reported to the user right where it's detected, -but often needs to be propagated up the call chain to a place that can -handle it. This can be done in various ways. - -The most flexible one is Error objects. See error.h for usage -information. - -Use the simplest suitable method to communicate success / failure to -callers. Stick to common methods: non-negative on success / -1 on -error, non-negative / -errno, non-null / null, or Error objects. - -Example: when a function returns a non-null pointer on success, and it -can fail only in one way (as far as the caller is concerned), returning -null on failure is just fine, and certainly simpler and a lot easier on -the eyes than propagating an Error object through an Error ** parameter. - -Example: when a function's callers need to report details on failure -only the function really knows, use Error **, and set suitable errors. - -Do not report an error to the user when you're also returning an error -for somebody else to handle. Leave the reporting to the place that -consumes the error returned. - -7.3 Handling errors - -Calling exit() is fine when handling configuration errors during -startup. It's problematic during normal operation. In particular, -monitor commands should never exit(). - -Do not call exit() or abort() to handle an error that can be triggered -by the guest (e.g., some unimplemented corner case in guest code -translation or device emulation). Guests should not be able to -terminate QEMU. - -Note that &error_fatal is just another way to exit(1), and &error_abort -is just another way to abort(). diff --git a/README b/README.rst similarity index 84% rename from README rename to README.rst index 441c33eb2f..7497709291 100644 --- a/README +++ b/README.rst @@ -1,5 +1,6 @@ - QEMU README - =========== +=========== +QEMU README +=========== QEMU is a generic and open source machine & userspace emulator and virtualizer. @@ -37,6 +38,9 @@ QEMU is multi-platform software intended to be buildable on all modern Linux platforms, OS-X, Win32 (via the Mingw64 toolchain) and a variety of other UNIX targets. The simple steps to build QEMU are: + +.. code-block:: shell + mkdir build cd build ../configure @@ -44,9 +48,9 @@ of other UNIX targets. The simple steps to build QEMU are: Additional information can also be found online via the QEMU website: - https://qemu.org/Hosts/Linux - https://qemu.org/Hosts/Mac - https://qemu.org/Hosts/W32 +* ``_ +* ``_ +* ``_ Submitting patches @@ -54,24 +58,29 @@ Submitting patches The QEMU source code is maintained under the GIT version control system. +.. code-block:: shell + git clone https://git.qemu.org/git/qemu.git When submitting patches, one common approach is to use 'git format-patch' and/or 'git send-email' to format & send the mail to the qemu-devel@nongnu.org mailing list. All patches submitted must contain a 'Signed-off-by' line from the author. Patches should follow the -guidelines set out in the HACKING and CODING_STYLE files. +guidelines set out in the CODING_STYLE.rst file. Additional information on submitting patches can be found online via the QEMU website - https://qemu.org/Contribute/SubmitAPatch - https://qemu.org/Contribute/TrivialPatches +* ``_ +* ``_ The QEMU website is also maintained under source control. +.. code-block:: shell + git clone https://git.qemu.org/git/qemu-web.git - https://www.qemu.org/2017/02/04/the-new-qemu-website-is-up/ + +* ``_ A 'git-publish' utility was created to make above process less cumbersome, and is highly recommended for making regular contributions, @@ -82,10 +91,12 @@ manually for once. For installation instructions, please go to - https://github.com/stefanha/git-publish +* ``_ The workflow with 'git-publish' is: +.. code-block:: shell + $ git checkout master -b my-feature $ # work on new commits, add your 'Signed-off-by' lines to each $ git publish @@ -95,6 +106,8 @@ back to it in the future. Sending v2: +.. code-block:: shell + $ git checkout my-feature # same topic branch $ # making changes to the commits (using 'git rebase', for example) $ git publish @@ -109,7 +122,7 @@ The QEMU project uses Launchpad as its primary upstream bug tracker. Bugs found when running code built from QEMU git or upstream released sources should be reported via: - https://bugs.launchpad.net/qemu/ +* ``_ If using QEMU via an operating system vendor pre-built binary package, it is preferable to report bugs to the vendor's own bug tracker first. If @@ -118,7 +131,7 @@ reported via launchpad. For additional information on bug reporting consult: - https://qemu.org/Contribute/ReportABug +* ``_ Contact @@ -127,13 +140,11 @@ Contact The QEMU community can be contacted in a number of ways, with the two main methods being email and IRC - - qemu-devel@nongnu.org - https://lists.nongnu.org/mailman/listinfo/qemu-devel - - #qemu on irc.oftc.net +* ``_ +* ``_ +* #qemu on irc.oftc.net Information on additional methods of contacting the community can be found online via the QEMU website: - https://qemu.org/Contribute/StartHere - --- End +* ``_ diff --git a/scripts/checkpatch.pl b/scripts/checkpatch.pl index d24c9441ee..aa9a354a0e 100755 --- a/scripts/checkpatch.pl +++ b/scripts/checkpatch.pl @@ -461,7 +461,7 @@ sub top_of_kernel_tree { my @tree_check = ( "COPYING", "MAINTAINERS", "Makefile", - "README", "docs", "VERSION", + "README.rst", "docs", "VERSION", "vl.c" );