Btrfs: Make async snapshot ioctl more generic

If we had reserved some bytes in struct btrfs_ioctl_vol_args, we
wouldn't have to create a new structure for async snapshot creation.

Here we convert async snapshot ioctl to use a more generic ABI, as
we'll add more ioctls for snapshots/subvolumes in the future, readonly
snapshots for example.

Signed-off-by: Li Zefan <lizf@cn.fujitsu.com>
Signed-off-by: Chris Mason <chris.mason@oracle.com>

2 files changed, 36 insertions, 22 deletions

diff --git a/fs/btrfs/ioctl.c b/fs/btrfs/ioctl.c
index 7cc2e8e075b4..f87552a1d7ea 100644
--- a/fs/btrfs/ioctl.c
+++ b/fs/btrfs/ioctl.c
@@ -947,31 +947,41 @@ out:
 
 static noinline int btrfs_ioctl_snap_create(struct file *file,
                                             void __user *arg, int subvol,
-                                            int async)
+                                            int v2)
 {
         struct btrfs_ioctl_vol_args *vol_args = NULL;
-        struct btrfs_ioctl_async_vol_args *async_vol_args = NULL;
+        struct btrfs_ioctl_vol_args_v2 *vol_args_v2 = NULL;
         char *name;
         u64 fd;
-        u64 transid = 0;
         int ret;
 
-        if (async) {
-                async_vol_args = memdup_user(arg, sizeof(*async_vol_args));
-                if (IS_ERR(async_vol_args))
-                        return PTR_ERR(async_vol_args);
+        if (v2) {
+                u64 transid = 0;
+                u64 *ptr = NULL;
 
-                name = async_vol_args->name;
-                fd = async_vol_args->fd;
-                async_vol_args->name[BTRFS_SNAPSHOT_NAME_MAX] = '\0';
+                vol_args_v2 = memdup_user(arg, sizeof(*vol_args_v2));
+                if (IS_ERR(vol_args_v2))
+                        return PTR_ERR(vol_args_v2);
+
+                if (vol_args_v2->flags & ~BTRFS_SUBVOL_CREATE_ASYNC) {
+                        ret = -EINVAL;
+                        goto out;
+                }
+
+                name = vol_args_v2->name;
+                fd = vol_args_v2->fd;
+                vol_args_v2->name[BTRFS_SUBVOL_NAME_MAX] = '\0';
+
+                if (vol_args_v2->flags & BTRFS_SUBVOL_CREATE_ASYNC)
+                        ptr = &transid;
 
                 ret = btrfs_ioctl_snap_create_transid(file, name, fd,
-                                                      subvol, &transid);
+                                                      subvol, ptr);
 
-                if (ret == 0 &&
+                if (ret == 0 && ptr &&
                     copy_to_user(arg +
-                                 offsetof(struct btrfs_ioctl_async_vol_args,
-                                          transid), &transid, sizeof(transid)))
+                                 offsetof(struct btrfs_ioctl_vol_args_v2,
+                                          transid), ptr, sizeof(*ptr)))
                         ret = -EFAULT;
         } else {
                 vol_args = memdup_user(arg, sizeof(*vol_args));
@@ -984,9 +994,9 @@ static noinline int btrfs_ioctl_snap_create(struct file *file,
                 ret = btrfs_ioctl_snap_create_transid(file, name, fd,
                                                       subvol, NULL);
         }
-
+out:
         kfree(vol_args);
-        kfree(async_vol_args);
+        kfree(vol_args_v2);
 
         return ret;
 }
@@ -2248,7 +2258,7 @@ long btrfs_ioctl(struct file *file, unsigned int
                 return btrfs_ioctl_getversion(file, argp);
         case BTRFS_IOC_SNAP_CREATE:
                 return btrfs_ioctl_snap_create(file, argp, 0, 0);
-        case BTRFS_IOC_SNAP_CREATE_ASYNC:
+        case BTRFS_IOC_SNAP_CREATE_V2:
                 return btrfs_ioctl_snap_create(file, argp, 0, 1);
         case BTRFS_IOC_SUBVOL_CREATE:
                 return btrfs_ioctl_snap_create(file, argp, 1, 0);
diff --git a/fs/btrfs/ioctl.h b/fs/btrfs/ioctl.h
index 17c99ebdf960..c344d12c646b 100644
--- a/fs/btrfs/ioctl.h
+++ b/fs/btrfs/ioctl.h
@@ -30,11 +30,15 @@ struct btrfs_ioctl_vol_args {
         char name[BTRFS_PATH_NAME_MAX + 1];
 };
 
-#define BTRFS_SNAPSHOT_NAME_MAX 4079
-struct btrfs_ioctl_async_vol_args {
+#define BTRFS_SUBVOL_CREATE_ASYNC       (1ULL << 0)
+
+#define BTRFS_SUBVOL_NAME_MAX 4039
+struct btrfs_ioctl_vol_args_v2 {
         __s64 fd;
         __u64 transid;
-        char name[BTRFS_SNAPSHOT_NAME_MAX + 1];
+        __u64 flags;
+        __u64 unused[4];
+        char name[BTRFS_SUBVOL_NAME_MAX + 1];
 };
 
 #define BTRFS_INO_LOOKUP_PATH_MAX 4080
@@ -187,6 +191,6 @@ struct btrfs_ioctl_space_args {
                                     struct btrfs_ioctl_space_args)
 #define BTRFS_IOC_START_SYNC _IOR(BTRFS_IOCTL_MAGIC, 24, __u64)
 #define BTRFS_IOC_WAIT_SYNC  _IOW(BTRFS_IOCTL_MAGIC, 22, __u64)
-#define BTRFS_IOC_SNAP_CREATE_ASYNC _IOW(BTRFS_IOCTL_MAGIC, 23, \
-                                   struct btrfs_ioctl_async_vol_args)
+#define BTRFS_IOC_SNAP_CREATE_V2 _IOW(BTRFS_IOCTL_MAGIC, 23, \
+                                   struct btrfs_ioctl_vol_args_v2)
 #endif