Commit ae6afc3f authored by jan Blunck's avatar jan Blunck Committed by Linus Torvalds
Browse files

vfs: introduce noop_llseek() 



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: default avatarJan 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: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent 09eeb1f5

fs/read_write.c

+17 −0
Original line number Diff line number Diff line
@@ -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;

include/linux/fs.h

+1 −0
Original line number Diff line number Diff line
@@ -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,

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