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ovl: store upper real file in ovl_file struct

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When an overlayfs file is opened as lower and then the file is copied up,
every operation on the overlayfs open file will open a temporary backing
file to the upper dentry and close it at the end of the operation.

Store the upper real file along side the original (lower) real file in
ovl_file instead of opening a temporary upper file on every operation.

Signed-off-by: Amir Goldstein <amir73il@gmail.com>
This commit is contained in:
Amir Goldstein 2024-10-14 17:25:26 +02:00
parent 87a8a76c34
commit 18e48d0e2c
1 changed files with 41 additions and 8 deletions
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49
fs/overlayfs/file.c
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@ -91,6 +91,7 @@ static int ovl_change_flags(struct file *file, unsigned int flags)
struct ovl_file {
struct file *realfile;
struct file *upperfile;
};
struct ovl_file *ovl_file_alloc(struct file *realfile)
@ -107,33 +108,65 @@ struct ovl_file *ovl_file_alloc(struct file *realfile)
void ovl_file_free(struct ovl_file *of)
{
fput(of->realfile);
if (of->upperfile)
fput(of->upperfile);
kfree(of);
}
static bool ovl_is_real_file(const struct file *realfile,
const struct path *realpath)
{
return file_inode(realfile) == d_inode(realpath->dentry);
}
static int ovl_real_fdget_path(const struct file *file, struct fd *real,
struct path *realpath)
{
struct ovl_file *of = file->private_data;
struct file *realfile = of->realfile;
real->word = (unsigned long)realfile;
real->word = 0;
if (WARN_ON_ONCE(!realpath->dentry))
return -EIO;
/* Has it been copied up since we'd opened it? */
if (unlikely(file_inode(realfile) != d_inode(realpath->dentry))) {
struct file *f = ovl_open_realfile(file, realpath);
if (IS_ERR(f))
return PTR_ERR(f);
real->word = (unsigned long)f | FDPUT_FPUT;
return 0;
/*
* If the realfile that we want is not where the data used to be at
* open time, either we'd been copied up, or it's an fsync of a
* metacopied file. We need the upperfile either way, so see if it
* is already opened and if it is not then open and store it.
*/
if (unlikely(!ovl_is_real_file(realfile, realpath))) {
struct file *upperfile = READ_ONCE(of->upperfile);
struct file *old;
if (!upperfile) { /* Nobody opened upperfile yet */
upperfile = ovl_open_realfile(file, realpath);
if (IS_ERR(upperfile))
return PTR_ERR(upperfile);
/* Store the upperfile for later */
old = cmpxchg_release(&of->upperfile, NULL, upperfile);
if (old) { /* Someone opened upperfile before us */
fput(upperfile);
upperfile = old;
}
}
/*
* Stored file must be from the right inode, unless someone's
* been corrupting the upper layer.
*/
if (WARN_ON_ONCE(!ovl_is_real_file(upperfile, realpath)))
return -EIO;
realfile = upperfile;
}
/* Did the flags change since open? */
if (unlikely((file->f_flags ^ realfile->f_flags) & ~OVL_OPEN_FLAGS))
return ovl_change_flags(realfile, file->f_flags);
real->word = (unsigned long)realfile;
return 0;
}