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ovl: Add helper ovl_already_copied_up()

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There are couple of places where we need to know if file is already copied
up (in lockless manner).  Right now its open coded and there are only two
conditions to check.  Soon this patch series will introduce another
condition to check and Amir wants to introduce one more.  So introduce a
helper instead to check this so that code is easier to read.

Signed-off-by: Vivek Goyal <vgoyal@redhat.com>
Reviewed-by: Amir Goldstein <amir73il@gmail.com>
Signed-off-by: Miklos Szeredi <mszeredi@redhat.com>
This commit is contained in:
Vivek Goyal
2018-05-11 11:49:28 -04:00
committed by Miklos Szeredi
parent 44d5bf109a
commit 2002df8536
3 changed files with 28 additions and 19 deletions
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26
fs/overlayfs/util.c
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@@ -377,13 +377,37 @@ struct file *ovl_path_open(struct path *path, int flags)
return dentry_open(path, flags | O_NOATIME, current_cred());
}
bool ovl_already_copied_up(struct dentry *dentry)
{
bool disconnected = dentry->d_flags & DCACHE_DISCONNECTED;
/*
* Check if copy-up has happened as well as for upper alias (in
* case of hard links) is there.
*
* Both checks are lockless:
* - false negatives: will recheck under oi->lock
* - false positives:
* + ovl_dentry_upper() uses memory barriers to ensure the
* upper dentry is up-to-date
* + ovl_dentry_has_upper_alias() relies on locking of
* upper parent i_rwsem to prevent reordering copy-up
* with rename.
*/
if (ovl_dentry_upper(dentry) &&
(ovl_dentry_has_upper_alias(dentry) || disconnected))
return true;
return false;
}
int ovl_copy_up_start(struct dentry *dentry)
{
struct ovl_inode *oi = OVL_I(d_inode(dentry));
int err;
err = mutex_lock_interruptible(&oi->lock);
if (!err && ovl_dentry_has_upper_alias(dentry)) {
if (!err && ovl_already_copied_up(dentry)) {
err = 1; /* Already copied up */
mutex_unlock(&oi->lock);
}