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libfs: Add simple_offset_empty() 

For simple filesystems that use directory offset mapping, rely
strictly on the directory offset map to tell when a directory has
no children.

After this patch is applied, the emptiness test holds only the RCU
read lock when the directory being tested has no children.

In addition, this adds another layer of confirmation that
simple_offset_add/remove() are working as expected.

Reviewed-by: Jan Kara <jack@suse.cz>
Signed-off-by: Chuck Lever <chuck.lever@oracle.com>
Link: https://lore.kernel.org/r/170820143463.6328.7872919188371286951.stgit@91.116.238.104.host.secureserver.net
Signed-off-by: Christian Brauner <brauner@kernel.org>
This commit is contained in:
Chuck Lever 2024-02-17 15:23:54 -05:00 committed by Christian Brauner
parent 7beea725a8
commit ecba88a3b3
3 changed files with 35 additions and 2 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

32
fs/libfs.c
View File

@ -313,6 +313,38 @@ void simple_offset_remove(struct offset_ctx *octx, struct dentry *dentry)
offset_set(dentry, 0);
}
/**
* simple_offset_empty - Check if a dentry can be unlinked
* @dentry: dentry to be tested
*
* Returns 0 if @dentry is a non-empty directory; otherwise returns 1.
*/
int simple_offset_empty(struct dentry *dentry)
{
struct inode *inode = d_inode(dentry);
struct offset_ctx *octx;
struct dentry *child;
unsigned long index;
int ret = 1;
if (!inode || !S_ISDIR(inode->i_mode))
return ret;
index = DIR_OFFSET_MIN;
octx = inode->i_op->get_offset_ctx(inode);
xa_for_each(&octx->xa, index, child) {
spin_lock(&child->d_lock);
if (simple_positive(child)) {
spin_unlock(&child->d_lock);
ret = 0;
break;
}
spin_unlock(&child->d_lock);
}
return ret;
}
/**
* simple_offset_rename_exchange - exchange rename with directory offsets
* @old_dir: parent of dentry being moved

1
include/linux/fs.h
View File

@ -3267,6 +3267,7 @@ struct offset_ctx {
void simple_offset_init(struct offset_ctx *octx);
int simple_offset_add(struct offset_ctx *octx, struct dentry *dentry);
void simple_offset_remove(struct offset_ctx *octx, struct dentry *dentry);
int simple_offset_empty(struct dentry *dentry);
int simple_offset_rename_exchange(struct inode *old_dir,
struct dentry *old_dentry,
struct inode *new_dir,

4
mm/shmem.c
View File

@ -3374,7 +3374,7 @@ static int shmem_unlink(struct inode *dir, struct dentry *dentry)
static int shmem_rmdir(struct inode *dir, struct dentry *dentry)
{
if (!simple_empty(dentry))
if (!simple_offset_empty(dentry))
return -ENOTEMPTY;
drop_nlink(d_inode(dentry));
@ -3431,7 +3431,7 @@ static int shmem_rename2(struct mnt_idmap *idmap,
return simple_offset_rename_exchange(old_dir, old_dentry,
new_dir, new_dentry);
if (!simple_empty(new_dentry))
if (!simple_offset_empty(new_dentry))
return -ENOTEMPTY;
if (flags & RENAME_WHITEOUT) {