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Documentation: seq_file: Document seq_open_private(), seq_release_private()

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Despite the fact that these functions have been around for years, they
are little used (only 15 uses in 13 files at the preseht time) even
though many other files use work-arounds to achieve the same result.

By documenting them, hopefully they will become more widely used.

Signed-off-by: Rob Jones <rob.jones@codethink.co.uk>
Acked-by: Steven Whitehouse <swhiteho@redhat.com>
Signed-off-by: Randy Dunlap <rdunlap@infradead.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
This commit is contained in:
Rob Jones 2014-09-07 11:24:40 -07:00 committed by Linus Torvalds
parent 6fef37c9a7
commit 77be4daf4e
1 changed files with 33 additions and 0 deletions
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33
Documentation/filesystems/seq_file.txt
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@ -235,6 +235,39 @@ be used for more than one file, you can store an arbitrary pointer in the
private field of the seq_file structure; that value can then be retrieved
by the iterator functions.
There is also a wrapper function to seq_open() called seq_open_private(). It
kmallocs a zero filled block of memory and stores a pointer to it in the
private field of the seq_file structure, returning 0 on success. The
block size is specified in a third parameter to the function, e.g.:
static int ct_open(struct inode *inode, struct file *file)
{
return seq_open_private(file, &ct_seq_ops,
sizeof(struct mystruct));
}
There is also a variant function, __seq_open_private(), which is functionally
identical except that, if successful, it returns the pointer to the allocated
memory block, allowing further initialisation e.g.:
static int ct_open(struct inode *inode, struct file *file)
{
struct mystruct *p =
__seq_open_private(file, &ct_seq_ops, sizeof(*p));
if (!p)
return -ENOMEM;
p->foo = bar; /* initialize my stuff */
...
p->baz = true;
return 0;
}
A corresponding close function, seq_release_private() is available which
frees the memory allocated in the corresponding open.
The other operations of interest - read(), llseek(), and release() - are
all implemented by the seq_file code itself. So a virtual file's
file_operations structure will look like: