[0/6] btrfs-progs: mkfs: introduce an experimental --subvol option

Message

Qu Wenruo Oct. 16, 2023, 4:38 a.m. UTC

Issue #42 (good number by the way) is suggesting a very useful feature
for rootfs image creation.

Currently we only support "mkfs.btrfs --rootdir" to fill the fs tree
with target directory, but there has no btrfs specific features
involved.

If we can create certain paths as subvolumes, not pure directories, it
can be very useful to create the whole btrfs image just by "mkfs.btrfs"

This series is the first step torwards this idea.

Now we have a new experimental option "--subvol" for mkfs.btrfs, but
with the following limits:

- No co-operation with --rootdir
  This requires --rootdir to have extra handling for any existing
  inodes.
  (Currently --rootdir assumes the fs tree is completely empty)

- No multiple --subvol options supports
  This requires us to collect and sort all the paths and start creating
  subvolumes from the shortest path.
  Furthermore this requires us to create subvolume under another
  subvolume.

Each limit would need a new series of patches to address, but this
series would already provide a working but not-that-useful
implementation of "--subvol" option, along with a basic test case for
it.

Qu Wenruo (6):
  btrfs-progs: enhance btrfs_mkdir() function
  btrfs-progs: enhance and rename btrfs_mksubvol() function
  btrfs-progs: enhance btrfs_create_root() function
  btrfs-progs: use a unified btrfs_make_subvol() implementation
  btrfs-progs: mkfs: introduce experimental --subvol option
  btrfs-progs: mkfs-tests: introduce a test case to verify --subvol
    option

 convert/main.c                             |  60 ++------
 kernel-shared/ctree.c                      | 106 ++++++--------
 kernel-shared/ctree.h                      |  12 +-
 kernel-shared/inode.c                      | 129 ++++++++++++-----
 kernel-shared/root-tree.c                  |  86 +++++++++++
 mkfs/common.c                              |  39 -----
 mkfs/common.h                              |   2 -
 mkfs/main.c                                | 103 ++++----------
 mkfs/rootdir.c                             | 157 +++++++++++++++++++++
 mkfs/rootdir.h                             |   1 +
 tests/mkfs-tests/031-subvol-option/test.sh |  39 +++++
 tune/convert-bgt.c                         |   3 +-
 tune/quota.c                               |   2 +-
 13 files changed, 473 insertions(+), 266 deletions(-)
 create mode 100755 tests/mkfs-tests/031-subvol-option/test.sh

--
2.42.0

Comments

Goffredo Baroncelli Oct. 19, 2023, 6:19 p.m. UTC | #1

Hi Qu,
On 16/10/2023 06.38, Qu Wenruo wrote:
> Issue #42 (good number by the way) is suggesting a very useful feature
> for rootfs image creation.
> 
> Currently we only support "mkfs.btrfs --rootdir" to fill the fs tree
> with target directory, but there has no btrfs specific features
> involved.
> 
> If we can create certain paths as subvolumes, not pure directories, it
> can be very useful to create the whole btrfs image just by "mkfs.btrfs"
> 
> This series is the first step torwards this idea.
> 
> Now we have a new experimental option "--subvol" for mkfs.btrfs, but
> with the following limits:


I have a suggestion and an enhancement request:
- why not use --mk-subvol? to me it seems more clear that a subvolume will be created
- add another option like --mk-default-subvolume that:
	- create a subvolume
	- make it the default.

The use case is the following: in btrfs it is easy make a snapshot, and move/rename/delete
subvolumes and snapshot. The only exception is the subvolid=5 (or /). You cannot delete it.
So if you want to do a snapshot of / and then rollback to this snapshot, it is complicated
because you cannot remove the original subvolume.

Starting from a subvolume different from subvolid=5 makes this easier.
  
> 
> - No co-operation with --rootdir
>    This requires --rootdir to have extra handling for any existing
>    inodes.
>    (Currently --rootdir assumes the fs tree is completely empty)
> 
> - No multiple --subvol options supports
>    This requires us to collect and sort all the paths and start creating
>    subvolumes from the shortest path.
>    Furthermore this requires us to create subvolume under another
>    subvolume.
> 
> Each limit would need a new series of patches to address, but this
> series would already provide a working but not-that-useful
> implementation of "--subvol" option, along with a basic test case for
> it.
> 
> Qu Wenruo (6):
>    btrfs-progs: enhance btrfs_mkdir() function
>    btrfs-progs: enhance and rename btrfs_mksubvol() function
>    btrfs-progs: enhance btrfs_create_root() function
>    btrfs-progs: use a unified btrfs_make_subvol() implementation
>    btrfs-progs: mkfs: introduce experimental --subvol option
>    btrfs-progs: mkfs-tests: introduce a test case to verify --subvol
>      option
> 
>   convert/main.c                             |  60 ++------
>   kernel-shared/ctree.c                      | 106 ++++++--------
>   kernel-shared/ctree.h                      |  12 +-
>   kernel-shared/inode.c                      | 129 ++++++++++++-----
>   kernel-shared/root-tree.c                  |  86 +++++++++++
>   mkfs/common.c                              |  39 -----
>   mkfs/common.h                              |   2 -
>   mkfs/main.c                                | 103 ++++----------
>   mkfs/rootdir.c                             | 157 +++++++++++++++++++++
>   mkfs/rootdir.h                             |   1 +
>   tests/mkfs-tests/031-subvol-option/test.sh |  39 +++++
>   tune/convert-bgt.c                         |   3 +-
>   tune/quota.c                               |   2 +-
>   13 files changed, 473 insertions(+), 266 deletions(-)
>   create mode 100755 tests/mkfs-tests/031-subvol-option/test.sh
> 
> --
> 2.42.0
>