From 77be4daf4e65eb1da70e6623ec61ecde62f5de95 Mon Sep 17 00:00:00 2001 From: Rob Jones Date: Sun, 7 Sep 2014 11:24:40 -0700 Subject: Documentation: seq_file: Document seq_open_private(), seq_release_private() 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 Acked-by: Steven Whitehouse Signed-off-by: Randy Dunlap Signed-off-by: Linus Torvalds --- Documentation/filesystems/seq_file.txt | 33 +++++++++++++++++++++++++++++++++ 1 file changed, 33 insertions(+) (limited to 'Documentation') diff --git a/Documentation/filesystems/seq_file.txt b/Documentation/filesystems/seq_file.txt index 1fe0ccb1af55..8ea3e90ace07 100644 --- a/Documentation/filesystems/seq_file.txt +++ b/Documentation/filesystems/seq_file.txt @@ -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: -- cgit v1.2.3-58-ga151