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Commit 7b1a14bb authored by Chris Mason's avatar Chris Mason
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Btrfs: fix acl caching 



Linus noticed the btrfs code to cache acls wasn't properly caching
a NULL acl when the inode didn't have any acls.  This meant the common
case of no acls resulted in expensive btree searches every time the
kernel checked permissions (which is quite often).

This is a modified version of Linus' original patch:

Properly set initial acl fields to BTRFS_ACL_NOT_CACHED in the inode.
This forces an acl lookup when permission checks are done.

Fix btrfs_get_acl to avoid lookups and locking when the inode acls fields
are set to null.

Fix btrfs_get_acl to use the right return value from __btrfs_getxattr
when deciding to cache a NULL acl.  It was storing a NULL acl when
__btrfs_getxattr return -ENOENT, but __btrfs_getxattr was actually returning
-ENODATA for this case.

Signed-off-by: default avatarChris Mason <chris.mason@oracle.com>
parent 21380931

fs/btrfs/acl.c

+13 −5
Original line number Diff line number Diff line
@@ -60,15 +60,20 @@ static struct posix_acl *btrfs_get_acl(struct inode *inode, int type) 
		return ERR_PTR(-EINVAL);

	}



	/* Handle the cached NULL acl case without locking */

	acl = ACCESS_ONCE(*p_acl);

	if (!acl)

		return acl;



	spin_lock(&inode->i_lock);

	if (*p_acl != BTRFS_ACL_NOT_CACHED)

		acl = posix_acl_dup(*p_acl);

	acl = *p_acl;

	if (acl != BTRFS_ACL_NOT_CACHED)

		acl = posix_acl_dup(acl);

	spin_unlock(&inode->i_lock);



	if (acl)

	if (acl != BTRFS_ACL_NOT_CACHED)

		return acl;





	size = __btrfs_getxattr(inode, name, "", 0);

	if (size > 0) {

		value = kzalloc(size, GFP_NOFS);
@@ -80,9 +85,12 @@ static struct posix_acl *btrfs_get_acl(struct inode *inode, int type) 
			btrfs_update_cached_acl(inode, p_acl, acl);

		}

		kfree(value);

	} else if (size == -ENOENT) {

	} else if (size == -ENOENT || size == -ENODATA || size == 0) {

		/* FIXME, who returns -ENOENT?  I think nobody */

		acl = NULL;

		btrfs_update_cached_acl(inode, p_acl, acl);

	} else {

		acl = ERR_PTR(-EIO);

	}



	return acl;

fs/btrfs/inode.c

+2 −2
Original line number Diff line number Diff line
@@ -3047,8 +3047,8 @@ static noinline void init_btrfs_i(struct inode *inode) 
{

	struct btrfs_inode *bi = BTRFS_I(inode);



	bi->i_acl = NULL;

	bi->i_default_acl = NULL;

	bi->i_acl = BTRFS_ACL_NOT_CACHED;

	bi->i_default_acl = BTRFS_ACL_NOT_CACHED;



	bi->generation = 0;

	bi->sequence = 0;