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vfs: allow custom EOF in generic_file_llseek code

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For ext3/4 htree directories, using the vfs llseek function with
SEEK_END goes to i_size like for any other file, but in reality
we want the maximum possible hash value.  Recent changes
in ext4 have cut & pasted generic_file_llseek() back into fs/ext4/dir.c,
but replicating this core code seems like a bad idea, especially
since the copy has already diverged from the vfs.

This patch updates generic_file_llseek_size to accept
both a custom maximum offset, and a custom EOF position.  With this
in place, ext4_dir_llseek can pass in the appropriate maximum hash
position for both maxsize and eof, and get what it wants.

As far as I know, this does not fix any bugs - nfs in the kernel
doesn't use SEEK_END, and I don't know of any user who does.  But
some ext4 folks seem keen on doing the right thing here, and I can't
really argue.

(Patch also fixes up some comments slightly)

Signed-off-by: Eric Sandeen <sandeen@redhat.com>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
This commit is contained in:
Eric Sandeen 2012-04-30 13:11:29 -05:00 committed by Al Viro
parent 4ea425b63a
commit e8b96eb503
4 changed files with 15 additions and 11 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

3
fs/ext3/dir.c
View File

@ -303,7 +303,8 @@ loff_t ext3_dir_llseek(struct file *file, loff_t offset, int origin)
if (likely(dx_dir))
return generic_file_llseek_size(file, offset, origin,
ext3_get_htree_eof(file));
ext3_get_htree_eof(file),
i_size_read(inode));
else
return generic_file_llseek(file, offset, origin);
}

3
fs/ext4/file.c
View File

@ -225,7 +225,8 @@ loff_t ext4_llseek(struct file *file, loff_t offset, int origin)
else
maxbytes = inode->i_sb->s_maxbytes;
return generic_file_llseek_size(file, offset, origin, maxbytes);
return generic_file_llseek_size(file, offset, origin,
maxbytes, i_size_read(inode));
}
const struct file_operations ext4_file_operations = {

18
fs/read_write.c
View File

@ -55,10 +55,11 @@ static loff_t lseek_execute(struct file *file, struct inode *inode,
* @file: file structure to seek on
* @offset: file offset to seek to
* @origin: type of seek
* @size: max size of file system
* @size: max size of this file in file system
* @eof: offset used for SEEK_END position
*
* This is a variant of generic_file_llseek that allows passing in a custom
* file size.
* maximum file size and a custom EOF position, for e.g. hashed directories
*
* Synchronization:
* SEEK_SET and SEEK_END are unsynchronized (but atomic on 64bit platforms)
@ -67,13 +68,13 @@ static loff_t lseek_execute(struct file *file, struct inode *inode,
*/
loff_t
generic_file_llseek_size(struct file *file, loff_t offset, int origin,
loff_t maxsize)
loff_t maxsize, loff_t eof)
{
struct inode *inode = file->f_mapping->host;
switch (origin) {
case SEEK_END:
offset += i_size_read(inode);
offset += eof;
break;
case SEEK_CUR:
/*
@ -99,7 +100,7 @@ generic_file_llseek_size(struct file *file, loff_t offset, int origin,
* 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 (offset >= i_size_read(inode))
if (offset >= eof)
return -ENXIO;
break;
case SEEK_HOLE:
@ -107,9 +108,9 @@ generic_file_llseek_size(struct file *file, loff_t offset, int origin,
* 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 (offset >= i_size_read(inode))
if (offset >= eof)
return -ENXIO;
offset = i_size_read(inode);
offset = eof;
break;
}
@ -132,7 +133,8 @@ loff_t generic_file_llseek(struct file *file, loff_t offset, int origin)
struct inode *inode = file->f_mapping->host;
return generic_file_llseek_size(file, offset, origin,
inode->i_sb->s_maxbytes);
inode->i_sb->s_maxbytes,
i_size_read(inode));
}
EXPORT_SYMBOL(generic_file_llseek);

2
include/linux/fs.h
View File

@ -2454,7 +2454,7 @@ 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_size(struct file *file, loff_t offset,
int origin, loff_t maxsize);
int origin, loff_t maxsize, loff_t eof);
extern int generic_file_open(struct inode * inode, struct file * filp);
extern int nonseekable_open(struct inode * inode, struct file * filp);