Re: [PATCH V3] seq_file: Document seq_open_private(), seq_release_private()

From: Rob Jones
Date: Tue Aug 26 2014 - 06:59:12 EST

Are there any other responses on this please? It seems pretty
uncontentious. Maybe everyone was at LinuxCon last week.

On 18/08/14 12:50, Steven Whitehouse wrote:

On 18/08/14 12:40, Rob Jones wrote:
Despite the fact that these functions have been around for years, they
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@xxxxxxxxxxxxxxx>
Acked-by: Steven Whitehouse <swhiteho@xxxxxxxxxx>


Documentation/filesystems/seq_file.txt | 33
1 file changed, 33 insertions(+)

diff --git a/Documentation/filesystems/seq_file.txt
index a1e2e0d..420fc0d 100644
--- a/Documentation/filesystems/seq_file.txt
+++ b/Documentation/filesystems/seq_file.txt
@@ -226,6 +226,39 @@ 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
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
+identical except that, if successful, it returns the pointer to the
+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() -
all implemented by the seq_file code itself. So a virtual file's
file_operations structure will look like:

Rob Jones
Codethink Ltd
tel:+44 161 236 5575
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