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240 lines
7.0 KiB
C
240 lines
7.0 KiB
C
/* -*- Mode: C++; tab-width: 4; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
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/* This Source Code Form is subject to the terms of the Mozilla Public
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* License, v. 2.0. If a copy of the MPL was not distributed with this
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* file, You can obtain one at http://mozilla.org/MPL/2.0/. */
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/*
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** prshma.h -- NSPR Anonymous Shared Memory
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**
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** NSPR provides an anonymous shared memory based on NSPR's PRFileMap
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** type. The anonymous file-mapped shared memory provides an inheritable
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** shared memory, as in: the child process inherits the shared memory.
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** Compare the file-mapped anonymous shared memory to to a named shared
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** memory described in prshm.h. The intent is to provide a shared
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** memory that is accessable only by parent and child processes. ...
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** It's a security thing.
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**
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** Depending on the underlying platform, the file-mapped shared memory
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** may be backed by a file. ... surprise! ... On some platforms, no
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** real file backs the shared memory. On platforms where the shared
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** memory is backed by a file, the file's name in the filesystem is
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** visible to other processes for only the duration of the creation of
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** the file, hopefully a very short time. This restricts processess
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** that do not inherit the shared memory from opening the file and
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** reading or writing its contents. Further, when all processes
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** using an anonymous shared memory terminate, the backing file is
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** deleted. ... If you are not paranoid, you're not paying attention.
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**
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** The file-mapped shared memory requires a protocol for the parent
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** process and child process to share the memory. NSPR provides two
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** protocols. Use one or the other; don't mix and match.
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**
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** In the first protocol, the job of passing the inheritable shared
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** memory is done via helper-functions with PR_CreateProcess(). In the
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** second protocol, the parent process is responsible for creating the
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** child process; the parent and child are mutually responsible for
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** passing a FileMap string. NSPR provides helper functions for
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** extracting data from the PRFileMap object. ... See the examples
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** below.
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**
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** Both sides should adhere strictly to the protocol for proper
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** operation. The pseudo-code below shows the use of a file-mapped
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** shared memory by a parent and child processes. In the examples, the
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** server creates the file-mapped shared memory, the client attaches to
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** it.
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**
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** First protocol.
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** Server:
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**
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** fm = PR_OpenAnonFileMap(dirName, size, FilemapProt);
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** addr = PR_MemMap(fm);
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** attr = PR_NewProcessAttr();
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** PR_ProcessAttrSetInheritableFileMap( attr, fm, shmname );
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** PR_CreateProcess(Client);
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** PR_DestroyProcessAttr(attr);
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** ... yadda ...
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** PR_MemUnmap( addr );
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** PR_CloseFileMap(fm);
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**
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**
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** Client:
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** ... started by server via PR_CreateProcess()
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** fm = PR_GetInheritedFileMap( shmname );
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** addr = PR_MemMap(fm);
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** ... yadda ...
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** PR_MemUnmap(addr);
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** PR_CloseFileMap(fm);
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**
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**
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** Second Protocol:
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** Server:
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**
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** fm = PR_OpenAnonFileMap(dirName, size, FilemapProt);
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** fmstring = PR_ExportFileMapAsString( fm );
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** addr = PR_MemMap(fm);
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** ... application specific technique to pass fmstring to child
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** ... yadda ... Server uses his own magic to create child
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** PR_MemUnmap( addr );
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** PR_CloseFileMap(fm);
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**
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**
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** Client:
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** ... started by server via his own magic
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** ... application specific technique to find fmstring from parent
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** fm = PR_ImportFileMapFromString( fmstring )
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** addr = PR_MemMap(fm);
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** ... yadda ...
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** PR_MemUnmap(addr);
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** PR_CloseFileMap(fm);
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**
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**
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** lth. 2-Jul-1999.
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**
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** Note: The second protocol was requested by NelsonB (7/1999); this is
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** to accomodate servers which already create their own child processes
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** using platform native methods.
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**
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*/
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#ifndef prshma_h___
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#define prshma_h___
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#include "prtypes.h"
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#include "prio.h"
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#include "prproces.h"
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PR_BEGIN_EXTERN_C
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/*
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** PR_OpenAnonFileMap() -- Creates an anonymous file-mapped shared memory
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**
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** Description:
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** PR_OpenAnonFileMap() creates an anonymous shared memory. If the
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** shared memory already exists, a handle is returned to that shared
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** memory object.
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**
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** On Unix platforms, PR_OpenAnonFileMap() uses 'dirName' as a
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** directory name, without the trailing '/', to contain the anonymous
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** file. A filename is generated for the name.
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**
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** On Windows platforms, dirName is ignored.
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**
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** Inputs:
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** dirName -- A directory name to contain the anonymous file.
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** size -- The size of the shared memory
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** prot -- How the shared memory is mapped. See prio.h
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**
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** Outputs:
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** PRFileMap *
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**
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** Returns:
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** Pointer to PRFileMap or NULL on error.
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**
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*/
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NSPR_API( PRFileMap *)
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PR_OpenAnonFileMap(
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const char *dirName,
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PRSize size,
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PRFileMapProtect prot
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);
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/*
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** PR_ProcessAttrSetInheritableFileMap() -- Prepare FileMap for export
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** to my children processes via PR_CreateProcess()
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**
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** Description:
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** PR_ProcessAttrSetInheritableFileMap() connects the PRFileMap to
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** PRProcessAttr with shmname. A subsequent call to PR_CreateProcess()
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** makes the PRFileMap importable by the child process.
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**
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** Inputs:
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** attr -- PRProcessAttr, used to pass data to PR_CreateProcess()
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** fm -- PRFileMap structure to be passed to the child process
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** shmname -- The name for the PRFileMap; used by child.
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**
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** Outputs:
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** PRFileMap *
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**
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** Returns:
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** PRStatus
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**
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*/
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NSPR_API(PRStatus)
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PR_ProcessAttrSetInheritableFileMap(
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PRProcessAttr *attr,
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PRFileMap *fm,
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const char *shmname
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);
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/*
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** PR_GetInheritedFileMap() -- Import a PRFileMap previously exported
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** by my parent process via PR_CreateProcess()
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**
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** Description:
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** PR_GetInheritedFileMap() retrieves a PRFileMap object exported from
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** its parent process via PR_CreateProcess().
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**
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** Inputs:
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** shmname -- The name provided to PR_ProcessAttrSetInheritableFileMap()
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**
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** Outputs:
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** PRFileMap *
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**
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** Returns:
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** PRFileMap pointer or NULL.
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**
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*/
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NSPR_API( PRFileMap *)
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PR_GetInheritedFileMap(
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const char *shmname
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);
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/*
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** PR_ExportFileMapAsString() -- Creates a string identifying a PRFileMap
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**
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** Description:
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** Creates an identifier, as a string, from a PRFileMap object
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** previously created with PR_OpenAnonFileMap().
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**
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** Inputs:
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** fm -- PRFileMap pointer to be represented as a string.
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** bufsize -- sizeof(buf)
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** buf -- a buffer of length PR_FILEMAP_STRING_BUFSIZE
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**
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** Outputs:
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** buf contains the stringized PRFileMap identifier
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**
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** Returns:
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** PRStatus
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**
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*/
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NSPR_API( PRStatus )
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PR_ExportFileMapAsString(
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PRFileMap *fm,
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PRSize bufsize,
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char *buf
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);
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#define PR_FILEMAP_STRING_BUFSIZE 128
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/*
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** PR_ImportFileMapFromString() -- Creates a PRFileMap from the identifying string
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**
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** Description:
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** PR_ImportFileMapFromString() creates a PRFileMap object from a
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** string previously created by PR_ExportFileMapAsString().
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**
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** Inputs:
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** fmstring -- string created by PR_ExportFileMapAsString()
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**
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** Returns:
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** PRFileMap pointer or NULL.
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**
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*/
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NSPR_API( PRFileMap * )
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PR_ImportFileMapFromString(
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const char *fmstring
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);
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PR_END_EXTERN_C
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#endif /* prshma_h___ */
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