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Subject[PATCHv2] btrfs: Introduce new BTRFS_IOC_SNAP_DESTROY_V2 ioctl
Date
From: Marcos Paulo de Souza <mpdesouza@suse.com>

This ioctl will be responsible for deleting a subvolume using it's id.
This can be used when a system has a file system mounted from a
subvolume, rather than the root file system, like below:

/
|- @subvol1
|- @subvol2
\- @subvol_default
If only @subvol_default is mounted, we have no path to reach
@subvol1 and @subvol2, thus no way to delete them.
This patch introduces a new flag to allow BTRFS_IOC_SNAP_DESTORY_V2
to delete subvolume using subvolid.

Also in this patch, export some functions, add BTRFS_SUBVOL_BY_ID flag
and add subvolid as a union member of name in struct btrfs_ioctl_vol_args_v2.

Signed-off-by: Marcos Paulo de Souza <mpdesouza@suse.com>
---
Changes from v1:
* make btrfs_ioctl_snap_destroy handle both SNAP_DESTROY and SNAP_DESTROY_V2
(suggested by Josef)
* Change BTRFS_SUBVOL_DELETE_BY_ID to BTRFS_SUBVOL_BY_ID (David)
* Send patches for btrfs-progs and xfstests along this change

fs/btrfs/ctree.h | 2 +
fs/btrfs/export.c | 4 +-
fs/btrfs/export.h | 5 ++
fs/btrfs/ioctl.c | 97 +++++++++++++++++++++++++++++++-------
fs/btrfs/super.c | 4 +-
include/uapi/linux/btrfs.h | 12 ++++-
6 files changed, 101 insertions(+), 23 deletions(-)

diff --git a/fs/btrfs/ctree.h b/fs/btrfs/ctree.h
index f90b82050d2d..5847a34b5146 100644
--- a/fs/btrfs/ctree.h
+++ b/fs/btrfs/ctree.h
@@ -3010,6 +3010,8 @@ int btrfs_defrag_leaves(struct btrfs_trans_handle *trans,
int btrfs_parse_options(struct btrfs_fs_info *info, char *options,
unsigned long new_flags);
int btrfs_sync_fs(struct super_block *sb, int wait);
+char *btrfs_get_subvol_name_from_objectid(struct btrfs_fs_info *fs_info,
+ u64 subvol_objectid);

static inline __printf(2, 3) __cold
void btrfs_no_printk(const struct btrfs_fs_info *fs_info, const char *fmt, ...)
diff --git a/fs/btrfs/export.c b/fs/btrfs/export.c
index 72e312cae69d..027411cdbae7 100644
--- a/fs/btrfs/export.c
+++ b/fs/btrfs/export.c
@@ -57,7 +57,7 @@ static int btrfs_encode_fh(struct inode *inode, u32 *fh, int *max_len,
return type;
}

-static struct dentry *btrfs_get_dentry(struct super_block *sb, u64 objectid,
+struct dentry *btrfs_get_dentry(struct super_block *sb, u64 objectid,
u64 root_objectid, u32 generation,
int check_generation)
{
@@ -152,7 +152,7 @@ static struct dentry *btrfs_fh_to_dentry(struct super_block *sb, struct fid *fh,
return btrfs_get_dentry(sb, objectid, root_objectid, generation, 1);
}

-static struct dentry *btrfs_get_parent(struct dentry *child)
+struct dentry *btrfs_get_parent(struct dentry *child)
{
struct inode *dir = d_inode(child);
struct btrfs_fs_info *fs_info = btrfs_sb(dir->i_sb);
diff --git a/fs/btrfs/export.h b/fs/btrfs/export.h
index 57488ecd7d4e..f981e8103d64 100644
--- a/fs/btrfs/export.h
+++ b/fs/btrfs/export.h
@@ -18,4 +18,9 @@ struct btrfs_fid {
u64 parent_root_objectid;
} __attribute__ ((packed));

+struct dentry *btrfs_get_dentry(struct super_block *sb, u64 objectid,
+ u64 root_objectid, u32 generation,
+ int check_generation);
+struct dentry *btrfs_get_parent(struct dentry *child);
+
#endif
diff --git a/fs/btrfs/ioctl.c b/fs/btrfs/ioctl.c
index 1b1b6ff855aa..889cb43149f9 100644
--- a/fs/btrfs/ioctl.c
+++ b/fs/btrfs/ioctl.c
@@ -28,6 +28,7 @@
#include <linux/iversion.h>
#include "ctree.h"
#include "disk-io.h"
+#include "export.h"
#include "transaction.h"
#include "btrfs_inode.h"
#include "print-tree.h"
@@ -2836,7 +2837,8 @@ static int btrfs_ioctl_get_subvol_rootref(struct file *file, void __user *argp)
}

static noinline int btrfs_ioctl_snap_destroy(struct file *file,
- void __user *arg)
+ void __user *arg,
+ bool destroy_v2)
{
struct dentry *parent = file->f_path.dentry;
struct btrfs_fs_info *fs_info = btrfs_sb(parent->d_sb);
@@ -2845,34 +2847,87 @@ static noinline int btrfs_ioctl_snap_destroy(struct file *file,
struct inode *inode;
struct btrfs_root *root = BTRFS_I(dir)->root;
struct btrfs_root *dest = NULL;
- struct btrfs_ioctl_vol_args *vol_args;
+ struct btrfs_ioctl_vol_args *vol_args = NULL;
+ struct btrfs_ioctl_vol_args_v2 *vol_args2 = NULL;
+ char *name, *name_ptr = NULL;
int namelen;
int err = 0;

- if (!S_ISDIR(dir->i_mode))
- return -ENOTDIR;
+ if (destroy_v2) {
+ vol_args2 = memdup_user(arg, sizeof(*vol_args2));
+ if (IS_ERR(vol_args2))
+ return PTR_ERR(vol_args2);

- vol_args = memdup_user(arg, sizeof(*vol_args));
- if (IS_ERR(vol_args))
- return PTR_ERR(vol_args);
+ if (vol_args2->subvolid == 0) {
+ err = -EINVAL;
+ goto out;
+ }

- vol_args->name[BTRFS_PATH_NAME_MAX] = '\0';
- namelen = strlen(vol_args->name);
- if (strchr(vol_args->name, '/') ||
- strncmp(vol_args->name, "..", namelen) == 0) {
- err = -EINVAL;
- goto out;
+ if (!(vol_args2->flags & BTRFS_SUBVOL_BY_ID)) {
+ err = -EINVAL;
+ goto out;
+ }
+
+ dentry = btrfs_get_dentry(fs_info->sb, BTRFS_FIRST_FREE_OBJECTID,
+ vol_args2->subvolid, 0, 0);
+ if (IS_ERR(dentry)) {
+ err = PTR_ERR(dentry);
+ goto out;
+ }
+
+ /*
+ * change the default parent since the subvolume being deleted
+ * can be outside of the current mount point
+ */
+ parent = btrfs_get_parent(dentry);
+
+ /*
+ * the only use of dentry was to get the parent, so we can
+ * release it now. Later on the dentry will be queried again to
+ * make sure the dentry will reside in the dentry cache
+ */
+ dput(dentry);
+ if (IS_ERR(parent)) {
+ err = PTR_ERR(parent);
+ goto out;
+ }
+ dir = d_inode(parent);
+
+ name_ptr = btrfs_get_subvol_name_from_objectid(fs_info, vol_args2->subvolid);
+ if (IS_ERR(name_ptr)) {
+ err = PTR_ERR(name_ptr);
+ goto free_parent;
+ }
+ name = (char *)kbasename(name_ptr);
+ namelen = strlen(name);
+ } else {
+ vol_args = memdup_user(arg, sizeof(*vol_args));
+ if (IS_ERR(vol_args))
+ return PTR_ERR(vol_args);
+
+ vol_args->name[BTRFS_PATH_NAME_MAX] = '\0';
+ namelen = strlen(vol_args->name);
+ if (strchr(vol_args->name, '/') ||
+ strncmp(vol_args->name, "..", namelen) == 0) {
+ err = -EINVAL;
+ goto out;
+ }
+ name = vol_args->name;
+ }
+
+ if (!S_ISDIR(dir->i_mode)) {
+ err = -ENOTDIR;
+ goto free_subvol_name;
}

err = mnt_want_write_file(file);
if (err)
- goto out;
-
+ goto free_subvol_name;

err = down_write_killable_nested(&dir->i_rwsem, I_MUTEX_PARENT);
if (err == -EINTR)
goto out_drop_write;
- dentry = lookup_one_len(vol_args->name, parent, namelen);
+ dentry = lookup_one_len(name, parent, namelen);
if (IS_ERR(dentry)) {
err = PTR_ERR(dentry);
goto out_unlock_dir;
@@ -2943,7 +2998,13 @@ static noinline int btrfs_ioctl_snap_destroy(struct file *file,
inode_unlock(dir);
out_drop_write:
mnt_drop_write_file(file);
+free_subvol_name:
+ kfree(name_ptr);
+free_parent:
+ if (destroy_v2)
+ dput(parent);
out:
+ kfree(vol_args2);
kfree(vol_args);
return err;
}
@@ -5464,7 +5525,9 @@ long btrfs_ioctl(struct file *file, unsigned int
case BTRFS_IOC_SUBVOL_CREATE_V2:
return btrfs_ioctl_snap_create_v2(file, argp, 1);
case BTRFS_IOC_SNAP_DESTROY:
- return btrfs_ioctl_snap_destroy(file, argp);
+ return btrfs_ioctl_snap_destroy(file, argp, false);
+ case BTRFS_IOC_SNAP_DESTROY_V2:
+ return btrfs_ioctl_snap_destroy(file, argp, true);
case BTRFS_IOC_SUBVOL_GETFLAGS:
return btrfs_ioctl_subvol_getflags(file, argp);
case BTRFS_IOC_SUBVOL_SETFLAGS:
diff --git a/fs/btrfs/super.c b/fs/btrfs/super.c
index a906315efd19..4a8ce475d906 100644
--- a/fs/btrfs/super.c
+++ b/fs/btrfs/super.c
@@ -1024,7 +1024,7 @@ static int btrfs_parse_subvol_options(const char *options, char **subvol_name,
return error;
}

-static char *get_subvol_name_from_objectid(struct btrfs_fs_info *fs_info,
+char *btrfs_get_subvol_name_from_objectid(struct btrfs_fs_info *fs_info,
u64 subvol_objectid)
{
struct btrfs_root *root = fs_info->tree_root;
@@ -1438,7 +1438,7 @@ static struct dentry *mount_subvol(const char *subvol_name, u64 subvol_objectid,
goto out;
}
}
- subvol_name = get_subvol_name_from_objectid(btrfs_sb(mnt->mnt_sb),
+ subvol_name = btrfs_get_subvol_name_from_objectid(btrfs_sb(mnt->mnt_sb),
subvol_objectid);
if (IS_ERR(subvol_name)) {
root = ERR_CAST(subvol_name);
diff --git a/include/uapi/linux/btrfs.h b/include/uapi/linux/btrfs.h
index 7a8bc8b920f5..d8619245f0dc 100644
--- a/include/uapi/linux/btrfs.h
+++ b/include/uapi/linux/btrfs.h
@@ -42,11 +42,14 @@ struct btrfs_ioctl_vol_args {

#define BTRFS_DEVICE_SPEC_BY_ID (1ULL << 3)

+#define BTRFS_SUBVOL_BY_ID (1ULL << 4)
+
#define BTRFS_VOL_ARG_V2_FLAGS_SUPPORTED \
(BTRFS_SUBVOL_CREATE_ASYNC | \
BTRFS_SUBVOL_RDONLY | \
BTRFS_SUBVOL_QGROUP_INHERIT | \
- BTRFS_DEVICE_SPEC_BY_ID)
+ BTRFS_DEVICE_SPEC_BY_ID | \
+ BTRFS_SUBVOL_BY_ID)

#define BTRFS_FSID_SIZE 16
#define BTRFS_UUID_SIZE 16
@@ -119,7 +122,10 @@ struct btrfs_ioctl_vol_args_v2 {
__u64 unused[4];
};
union {
- char name[BTRFS_SUBVOL_NAME_MAX + 1];
+ union {
+ char name[BTRFS_SUBVOL_NAME_MAX + 1];
+ __u64 subvolid;
+ };
__u64 devid;
};
};
@@ -949,5 +955,7 @@ enum btrfs_err_code {
struct btrfs_ioctl_get_subvol_rootref_args)
#define BTRFS_IOC_INO_LOOKUP_USER _IOWR(BTRFS_IOCTL_MAGIC, 62, \
struct btrfs_ioctl_ino_lookup_user_args)
+#define BTRFS_IOC_SNAP_DESTROY_V2 _IOW(BTRFS_IOCTL_MAGIC, 63, \
+ struct btrfs_ioctl_vol_args_v2)

#endif /* _UAPI_LINUX_BTRFS_H */
--
2.24.0
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