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btrfs-progs: props: don't translate value of compression=none 

Currently, if user specifies value 'no' or 'none' on the command line,
it gets translated to an empty value that is passed to kernel. There was
a change in kernel 5.14 done by commit 5548c8c6f55b ("btrfs: props:
change how empty value is interpreted") that changes the behaviour
in that case.

The empty value is supposed to mean 'the default value' for any
property. For compression there is a need to distinguish resetting the
value and also setting the NOCOMPRESS property. The translation to empty
value makes that impossible.

The explanation and behaviour copied from the kernel patch:

    Old behaviour:

      $ lsattr file
      ---------------------- file
      # the NOCOMPRESS bit is set
      $ btrfs prop set file compression ''
      $ lsattr file
      ---------------------m file

    This is equivalent to 'btrfs prop set file compression no' in current
    btrfs-progs as the 'no' or 'none' values are translated to an empty
    string.

    This is where the new behaviour is different: empty string drops the
    compression flag (-c) and nocompress (-m):

      $ lsattr file
      ---------------------- file
      # No change
      $ btrfs prop set file compression ''
      $ lsattr file
      ---------------------- file
      $ btrfs prop set file compression lzo
      $ lsattr file
      --------c------------- file
      $ btrfs prop get file compression
      compression=lzo
      $ btrfs prop set file compression ''
      # Reset to the initial state
      $ lsattr file
      ---------------------- file
      # Set NOCOMPRESS bit
      $ btrfs prop set file compression no
      $ lsattr file
      ---------------------m file

    This obviously brings problems with backward compatibility, so this
    patch should not be backported without making sure the updated
    btrfs-progs are also used and that scripts have been updated to use the
    new semantics.

    Summary:

    - old kernel:
      no, none, "" - set NOCOMPRESS bit
    - new kernel:
      no, none - set NOCOMPRESS bit
      "" - drop all compression flags, ie. COMPRESS and NOCOMPRESS

Signed-off-by: Li Zhang <zhanglikernel@gmail.com>
[ update changelog ]
Signed-off-by: David Sterba <dsterba@suse.com>
This commit is contained in:
Li Zhang 2022-01-16 16:52:43 +08:00 committed by David Sterba
parent fd4bab06a4
commit 7781d1a2da
2 changed files with 5 additions and 3 deletions
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6
Documentation/btrfs-property.rst
View File

@ -47,7 +47,11 @@ get [-t <type>] <object> [<name>]
device as object. For a mounted filesystem, specify a mount point.
compression
compression algorithm set for an inode, possible values: *lzo*, *zlib*, *zstd*.
To disable compression use "" (empty string), *no* or *none*.
To disable compression use *no* or *none*. Empty value resets the
property and sets a default value.
.. note::
This has changed in version 5.18 of btrfs-progs and
requires kernel 5.14 or newer to work.
list [-t <type>] <object>
Lists available properties with their descriptions for the given object.

2
cmds/property.c
View File

@ -190,8 +190,6 @@ static int prop_compression(enum prop_object_type type,
xattr_name[XATTR_BTRFS_PREFIX_LEN + strlen(name)] = '\0';
if (value) {
if (strcmp(value, "no") == 0 || strcmp(value, "none") == 0)
value = "";
sret = fsetxattr(fd, xattr_name, value, strlen(value), 0);
} else {
sret = fgetxattr(fd, xattr_name, NULL, 0);