From ae6afc3f5cf53fb97bac2d0a209bb465952742e7 Mon Sep 17 00:00:00 2001 From: jan Blunck Date: Wed, 26 May 2010 14:44:48 -0700 Subject: [PATCH 1/1] 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: Jan Blunck Cc: Frederic Weisbecker Cc: Christoph Hellwig Cc: Al Viro Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- fs/read_write.c | 17 +++++++++++++++++ include/linux/fs.h | 1 + 2 files changed, 18 insertions(+) diff --git a/fs/read_write.c b/fs/read_write.c index 113386d6fd2d..9c0485236e68 100644 --- a/fs/read_write.c +++ b/fs/read_write.c @@ -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; diff --git a/include/linux/fs.h b/include/linux/fs.h index b336cb9ca9a0..9682d52d1507 100644 --- a/include/linux/fs.h +++ b/include/linux/fs.h @@ -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, -- 2.39.2