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ovl: support stacked SEEK_HOLE/SEEK_DATA

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Overlay file f_pos is the master copy that is preserved
through copy up and modified on read/write, but only real
fs knows how to SEEK_HOLE/SEEK_DATA and real fs may impose
limitations that are more strict than ->s_maxbytes for specific
files, so we use the real file to perform seeks.

We do not call real fs for SEEK_CUR:0 query and for SEEK_SET:0
requests.

Fixes: d1d04ef857 ("ovl: stack file ops")
Reported-by: Eddie Horng <eddiehorng.tw@gmail.com>
Signed-off-by: Amir Goldstein <amir73il@gmail.com>
Signed-off-by: Miklos Szeredi <mszeredi@redhat.com>
This commit is contained in:
Amir Goldstein 2019-02-27 13:32:11 +02:00 committed by Miklos Szeredi
parent 3428030da0
commit 9e46b840c7
1 changed files with 40 additions and 4 deletions
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44
fs/overlayfs/file.c
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@ -144,11 +144,47 @@ static int ovl_release(struct inode *inode, struct file *file)
static loff_t ovl_llseek(struct file *file, loff_t offset, int whence)
{
struct inode *realinode = ovl_inode_real(file_inode(file));
struct inode *inode = file_inode(file);
struct fd real;
const struct cred *old_cred;
ssize_t ret;
return generic_file_llseek_size(file, offset, whence,
realinode->i_sb->s_maxbytes,
i_size_read(realinode));
/*
* The two special cases below do not need to involve real fs,
* so we can optimizing concurrent callers.
*/
if (offset == 0) {
if (whence == SEEK_CUR)
return file->f_pos;
if (whence == SEEK_SET)
return vfs_setpos(file, 0, 0);
}
ret = ovl_real_fdget(file, &real);
if (ret)
return ret;
/*
* Overlay file f_pos is the master copy that is preserved
* through copy up and modified on read/write, but only real
* fs knows how to SEEK_HOLE/SEEK_DATA and real fs may impose
* limitations that are more strict than ->s_maxbytes for specific
* files, so we use the real file to perform seeks.
*/
inode_lock(inode);
real.file->f_pos = file->f_pos;
old_cred = ovl_override_creds(inode->i_sb);
ret = vfs_llseek(real.file, offset, whence);
revert_creds(old_cred);
file->f_pos = real.file->f_pos;
inode_unlock(inode);
fdput(real);
return ret;
}
static void ovl_file_accessed(struct file *file)