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vfs: introduce noop_llseek()

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This is an implementation of ->llseek useable for the rare special case
when userspace expects the seek to succeed but the (device) file is
actually not able to perform the seek.  In this case you use noop_llseek()
instead of falling back to the default implementation of ->llseek.

Signed-off-by: Jan Blunck <jblunck@suse.de>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Christoph Hellwig <hch@lst.de>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
This commit is contained in:
jan Blunck 2010-05-26 14:44:48 -07:00 committed by Linus Torvalds
parent 09eeb1f5f4
commit ae6afc3f5c
2 changed files with 18 additions and 0 deletions
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17
fs/read_write.c
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@ -97,6 +97,23 @@ loff_t generic_file_llseek(struct file *file, loff_t offset, int origin)
}
EXPORT_SYMBOL(generic_file_llseek);
/**
* noop_llseek - No Operation Performed llseek implementation
* @file: file structure to seek on
* @offset: file offset to seek to
* @origin: type of seek
*
* This is an implementation of ->llseek useable for the rare special case when
* userspace expects the seek to succeed but the (device) file is actually not
* able to perform the seek. In this case you use noop_llseek() instead of
* falling back to the default implementation of ->llseek.
*/
loff_t noop_llseek(struct file *file, loff_t offset, int origin)
{
return file->f_pos;
}
EXPORT_SYMBOL(noop_llseek);
loff_t no_llseek(struct file *file, loff_t offset, int origin)
{
return -ESPIPE;

1
include/linux/fs.h
View file

@ -2228,6 +2228,7 @@ extern long do_splice_direct(struct file *in, loff_t *ppos, struct file *out,
extern void
file_ra_state_init(struct file_ra_state *ra, struct address_space *mapping);
extern loff_t noop_llseek(struct file *file, loff_t offset, int origin);
extern loff_t no_llseek(struct file *file, loff_t offset, int origin);
extern loff_t generic_file_llseek(struct file *file, loff_t offset, int origin);
extern loff_t generic_file_llseek_unlocked(struct file *file, loff_t offset,