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fs: add must_set_pos()

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Add a new must_set_pos() helper. We will use it in follow-up patches.
Temporarily mark it as unused. This is only done to keep the diff small
and reviewable.

Link: https://lore.kernel.org/r/20240830-vfs-file-f_version-v1-6-6d3e4816aa7b@kernel.org
Reviewed-by: Jan Kara <jack@suse.cz>
Reviewed-by: Jeff Layton <jlayton@kernel.org>
Signed-off-by: Christian Brauner <brauner@kernel.org>
This commit is contained in:
Christian Brauner 2024-08-30 15:04:47 +02:00
parent d095a5be75
commit b8c7451928
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GPG Key ID: 91C61BC06578DCA2
1 changed files with 54 additions and 0 deletions
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54
fs/read_write.c
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@ -85,6 +85,60 @@ loff_t vfs_setpos(struct file *file, loff_t offset, loff_t maxsize)
}
EXPORT_SYMBOL(vfs_setpos);
/**
* must_set_pos - check whether f_pos has to be updated
* @file: file to seek on
* @offset: offset to use
* @whence: type of seek operation
* @eof: end of file
*
* Check whether f_pos needs to be updated and update @offset according
* to @whence.
*
* Return: 0 if f_pos doesn't need to be updated, 1 if f_pos has to be
* updated, and negative error code on failure.
*/
static __maybe_unused int must_set_pos(struct file *file, loff_t *offset,
int whence, loff_t eof)
{
switch (whence) {
case SEEK_END:
*offset += eof;
break;
case SEEK_CUR:
/*
* Here we special-case the lseek(fd, 0, SEEK_CUR)
* position-querying operation. Avoid rewriting the "same"
* f_pos value back to the file because a concurrent read(),
* write() or lseek() might have altered it
*/
if (*offset == 0) {
*offset = file->f_pos;
return 0;
}
break;
case SEEK_DATA:
/*
* In the generic case the entire file is data, so as long as
* offset isn't at the end of the file then the offset is data.
*/
if ((unsigned long long)*offset >= eof)
return -ENXIO;
break;
case SEEK_HOLE:
/*
* There is a virtual hole at the end of the file, so as long as
* offset isn't i_size or larger, return i_size.
*/
if ((unsigned long long)*offset >= eof)
return -ENXIO;
*offset = eof;
break;
}
return 1;
}
/**
* generic_file_llseek_size - generic llseek implementation for regular files
* @file: file structure to seek on