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btrfs: sysfs: Add entry which shows if rmdir can work on subvolumes 

Deletion of a subvolume by rmdir(2) has become allowed by the
'commit cd2decf640b1 ("btrfs: Allow rmdir(2) to delete an empty
subvolume")'.

It is a kind of new feature and this commits add a sysfs entry

  /sys/fs/btrfs/features/rmdir_subvol

to indicate the availability of the feature so that a user program
(e.g. fstests) can detect it.

Prior to this commit, all entries in /sys/fs/btrfs/features are feature
which depend on feature bits of superblock (i.e. each feature affects
on-disk format) and managed by attribute_group "btrfs_feature_attr_group".
For each fs, entries in /sys/fs/btrfs/UUID/features indicate which
features are enabled (or can be changed online) for the fs.

However, rmdir_subvol feature only depends on kernel module. Therefore
new attribute_group "btrfs_static_feature_attr_group" is introduced and
sysfs_merge_group() is used to share /sys/fs/btrfs/features directory.
Features in "btrfs_static_feature_attr_group" won't be listed in each
/sys/fs/btrfs/UUID/features.

Signed-off-by: Tomohiro Misono <misono.tomohiro@jp.fujitsu.com>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>
This commit is contained in:
Misono Tomohiro 2018-05-17 14:24:51 +09:00 committed by David Sterba
parent 6c52157fa9
commit f902bd3a5e
1 changed files with 39 additions and 0 deletions
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39
fs/btrfs/sysfs.c
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@ -210,12 +210,42 @@ static struct attribute *btrfs_supported_feature_attrs[] = {
NULL
};
/*
* Features which depend on feature bits and may differ between each fs.
*
* /sys/fs/btrfs/features lists all available features of this kernel while
* /sys/fs/btrfs/UUID/features shows features of the fs which are enabled or
* can be changed online.
*/
static const struct attribute_group btrfs_feature_attr_group = {
.name = "features",
.is_visible = btrfs_feature_visible,
.attrs = btrfs_supported_feature_attrs,
};
static ssize_t rmdir_subvol_show(struct kobject *kobj,
struct kobj_attribute *ka, char *buf)
{
return snprintf(buf, PAGE_SIZE, "0\n");
}
BTRFS_ATTR(static_feature, rmdir_subvol, rmdir_subvol_show);
static struct attribute *btrfs_supported_static_feature_attrs[] = {
BTRFS_ATTR_PTR(static_feature, rmdir_subvol),
NULL
};
/*
* Features which only depend on kernel version.
*
* These are listed in /sys/fs/btrfs/features along with
* btrfs_feature_attr_group
*/
static const struct attribute_group btrfs_static_feature_attr_group = {
.name = "features",
.attrs = btrfs_supported_static_feature_attrs,
};
static ssize_t btrfs_show_u64(u64 *value_ptr, spinlock_t *lock, char *buf)
{
u64 val;
@ -901,8 +931,15 @@ int __init btrfs_init_sysfs(void)
ret = sysfs_create_group(&btrfs_kset->kobj, &btrfs_feature_attr_group);
if (ret)
goto out2;
ret = sysfs_merge_group(&btrfs_kset->kobj,
&btrfs_static_feature_attr_group);
if (ret)
goto out_remove_group;
return 0;
out_remove_group:
sysfs_remove_group(&btrfs_kset->kobj, &btrfs_feature_attr_group);
out2:
debugfs_remove_recursive(btrfs_debugfs_root_dentry);
out1:
@ -913,6 +950,8 @@ out1:
void __cold btrfs_exit_sysfs(void)
{
sysfs_unmerge_group(&btrfs_kset->kobj,
&btrfs_static_feature_attr_group);
sysfs_remove_group(&btrfs_kset->kobj, &btrfs_feature_attr_group);
kset_unregister(btrfs_kset);
debugfs_remove_recursive(btrfs_debugfs_root_dentry);