Re: [PATCH v2 3/5] fs, xfs: introduce FALLOC_FL_UNSEAL_BLOCK_MAP

Darrick J. Wong
2017-08-04T20:03:44Z

On Thu, Aug 03, 2017 at 07:28:23PM -0700, Dan Williams wrote:
> Provide an explicit fallocate operation type for clearing the
> S_IOMAP_IMMUTABLE flag. Like the enable case it requires CAP_IMMUTABLE
> and it can only be performed while no process has the file mapped.
>
> Cc: Jan Kara <jack@suse.cz>
> Cc: Jeff Moyer <jmoyer@redhat.com>
> Cc: Christoph Hellwig <hch@lst.de>
> Cc: Ross Zwisler <ross.zwisler@linux.intel.com>
> Cc: Alexander Viro <viro@zeniv.linux.org.uk>
> Cc: "Darrick J. Wong" <darrick.wong@oracle.com>
> Suggested-by: Dave Chinner <david@fromorbit.com>
> Signed-off-by: Dan Williams <dan.j.williams@intel.com>
> ---
> fs/open.c | 17 +++++++++++------
> fs/xfs/xfs_bmap_util.c | 42 ++++++++++++++++++++++++++++++++++++++++++
> fs/xfs/xfs_bmap_util.h | 3 +++
> fs/xfs/xfs_file.c | 4 +++-
> include/linux/falloc.h | 3 ++-
> include/uapi/linux/falloc.h | 1 +
> 6 files changed, 62 insertions(+), 8 deletions(-)
>
> diff --git a/fs/open.c b/fs/open.c
> index e3aae59785ae..ccfd8d3becc8 100644
> --- a/fs/open.c
> +++ b/fs/open.c
> @@ -274,13 +274,17 @@ int vfs_fallocate(struct file *file, int mode, loff_t offset, loff_t len)
> return -EINVAL;
>
> /*
> - * Seal block map operation should only be used exclusively, and
> - * with the IMMUTABLE capability.
> + * Seal/unseal block map operations should only be used
> + * exclusively, and with the IMMUTABLE capability.
> */
> - if (mode & FALLOC_FL_SEAL_BLOCK_MAP) {
> + if (mode & (FALLOC_FL_SEAL_BLOCK_MAP | FALLOC_FL_UNSEAL_BLOCK_MAP)) {
> if (!capable(CAP_LINUX_IMMUTABLE))
> return -EPERM;
> - if (mode & ~FALLOC_FL_SEAL_BLOCK_MAP)
> + if (mode == (FALLOC_FL_SEAL_BLOCK_MAP
> + | FALLOC_FL_UNSEAL_BLOCK_MAP))
> + return -EINVAL;
> + if (mode & ~(FALLOC_FL_SEAL_BLOCK_MAP
> + | FALLOC_FL_UNSEAL_BLOCK_MAP))
> return -EINVAL;
> }
>
> @@ -303,9 +307,10 @@ int vfs_fallocate(struct file *file, int mode, loff_t offset, loff_t len)
> return -ETXTBSY;
>
> /*
> - * We cannot allow any allocation changes on an iomap immutable file
> + * We cannot allow any allocation changes on an iomap immutable
> + * file, but we can allow clearing the immutable state.
> */
> - if (IS_IOMAP_IMMUTABLE(inode))
> + if (IS_IOMAP_IMMUTABLE(inode) && !(mode & FALLOC_FL_UNSEAL_BLOCK_MAP))
> return -ETXTBSY;
>
> /*
> diff --git a/fs/xfs/xfs_bmap_util.c b/fs/xfs/xfs_bmap_util.c
> index 46d8eb9e19fc..70ac2d33ab27 100644
> --- a/fs/xfs/xfs_bmap_util.c
> +++ b/fs/xfs/xfs_bmap_util.c
> @@ -1494,6 +1494,48 @@ xfs_seal_file_space(
> return error;
> }
>
> +int
> +xfs_unseal_file_space(
> + struct xfs_inode *ip,
> + xfs_off_t offset,
> + xfs_off_t len)
> +{
> + struct inode *inode = VFS_I(ip);
> + struct address_space *mapping = inode->i_mapping;
> + int error;
> +
> + ASSERT(xfs_isilocked(ip, XFS_MMAPLOCK_EXCL));

Same assert-on-the-iolock comment as the previous patch.

> +
> + if (offset)
> + return -EINVAL;
> +
> + xfs_ilock(ip, XFS_ILOCK_EXCL);
> + /*
> + * It does not make sense to unseal less than the full range of
> + * the file.
> + */
> + error = -EINVAL;
> + if (len < i_size_read(inode))
> + goto out_unlock;

Hmm, should we be picky and require len == i_size_read() here?

> + /*
> + * Provide safety against one thread changing the policy of not
> + * requiring fsync/msync (for block allocations) behind another
> + * thread's back.
> + */
> + error = -EBUSY;
> + if (mapping_mapped(mapping))
> + goto out_unlock;
> +
> + inode->i_flags &= ~S_IOMAP_IMMUTABLE;

It occurred to me, should we jump out early from the seal/unseal
operations if the flag state matches whatever the user is asking for?
This is perhaps not necessary for unseal since we don't do a lot of
work.

--D

> + error = 0;
> +
> +out_unlock:
> + xfs_iunlock(ip, XFS_ILOCK_EXCL);
> +
> + return error;
> +}
> +
> /*
> * @next_fsb will keep track of the extent currently undergoing shift.
> * @stop_fsb will keep track of the extent at which we have to stop.
> diff --git a/fs/xfs/xfs_bmap_util.h b/fs/xfs/xfs_bmap_util.h
> index 5115a32a2483..b64653a75942 100644
> --- a/fs/xfs/xfs_bmap_util.h
> +++ b/fs/xfs/xfs_bmap_util.h
> @@ -62,6 +62,9 @@ int xfs_insert_file_space(struct xfs_inode *, xfs_off_t offset,
> xfs_off_t len);
> int xfs_seal_file_space(struct xfs_inode *, xfs_off_t offset,
> xfs_off_t len);
> +int xfs_unseal_file_space(struct xfs_inode *, xfs_off_t offset,
> + xfs_off_t len);
> +
>
> /* EOF block manipulation functions */
> bool xfs_can_free_eofblocks(struct xfs_inode *ip, bool force);
> diff --git a/fs/xfs/xfs_file.c b/fs/xfs/xfs_file.c
> index e21121530a90..833f77700be2 100644
> --- a/fs/xfs/xfs_file.c
> +++ b/fs/xfs/xfs_file.c
> @@ -740,7 +740,7 @@ xfs_file_write_iter(
> (FALLOC_FL_KEEP_SIZE | FALLOC_FL_PUNCH_HOLE | \
> FALLOC_FL_COLLAPSE_RANGE | FALLOC_FL_ZERO_RANGE | \
> FALLOC_FL_INSERT_RANGE | FALLOC_FL_UNSHARE_RANGE | \
> - FALLOC_FL_SEAL_BLOCK_MAP)
> + FALLOC_FL_SEAL_BLOCK_MAP | FALLOC_FL_UNSEAL_BLOCK_MAP)
>
> STATIC long
> xfs_file_fallocate(
> @@ -840,6 +840,8 @@ xfs_file_fallocate(
> XFS_BMAPI_PREALLOC);
> } else if (mode & FALLOC_FL_SEAL_BLOCK_MAP) {
> error = xfs_seal_file_space(ip, offset, len);
> + } else if (mode & FALLOC_FL_UNSEAL_BLOCK_MAP) {
> + error = xfs_unseal_file_space(ip, offset, len);
> } else
> error = xfs_alloc_file_space(ip, offset, len,
> XFS_BMAPI_PREALLOC);
> diff --git a/include/linux/falloc.h b/include/linux/falloc.h
> index 48546c6fbec7..b22c1368ed1e 100644
> --- a/include/linux/falloc.h
> +++ b/include/linux/falloc.h
> @@ -27,6 +27,7 @@ struct space_resv {
> FALLOC_FL_ZERO_RANGE | \
> FALLOC_FL_INSERT_RANGE | \
> FALLOC_FL_UNSHARE_RANGE | \
> - FALLOC_FL_SEAL_BLOCK_MAP)
> + FALLOC_FL_SEAL_BLOCK_MAP | \
> + FALLOC_FL_UNSEAL_BLOCK_MAP)
>
> #endif /* _FALLOC_H_ */
> diff --git a/include/uapi/linux/falloc.h b/include/uapi/linux/falloc.h
> index 39076975bf6f..a4949e1a2dae 100644
> --- a/include/uapi/linux/falloc.h
> +++ b/include/uapi/linux/falloc.h
> @@ -95,4 +95,5 @@
> * with the punch, zero, collapse, or insert range modes.
> */
> #define FALLOC_FL_SEAL_BLOCK_MAP 0x080
> +#define FALLOC_FL_UNSEAL_BLOCK_MAP 0x100
> #endif /* _UAPI_FALLOC_H_ */
>
> --
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