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bcachefs: don't expose "read_only" as a mount option

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When "read_only" is exposed as a mount option, it is redundant with the
standard option "ro" and gives users multiple ways to specify that a
bcachefs filesystem should be mounted read-only. This presents the risk
of having inconsistent options specified.

This can be seen when remounting a read-only filesystem in read-write
mode, using mount(8) from util-linux. Because mount(8) parses the
existing mount options from `/proc/mounts` and applies them when
remounting, it can end up applying both "read_only" and "rw":

$ mount img -o ro /mnt
$ strace mount -o remount,rw /mnt
...
fsconfig(4, FSCONFIG_SET_FLAG, "read_only", NULL, 0) = 0
fsconfig(4, FSCONFIG_SET_FLAG, "rw", NULL, 0) = 0
...

Making "read_only" no longer a mount option means this edge case cannot
occur.

Fixes: 62719cf33c3a ("bcachefs: Fix nochanges/read_only interaction")
Signed-off-by: Thomas Bertschinger <tahbertschinger@gmail.com>
Signed-off-by: Kent Overstreet <kent.overstreet@linux.dev>
This commit is contained in:
Thomas Bertschinger 2024-05-26 13:08:20 -06:00 committed by Kent Overstreet
parent 03ec0927fa
commit babe30fe8d
1 changed files with 1 additions and 1 deletions
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2
fs/bcachefs/opts.h
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@ -406,7 +406,7 @@ enum fsck_err_opts {
BCH2_NO_SB_OPT, BCH_SB_SECTOR, \
"offset", "Sector offset of superblock") \
x(read_only, u8, \
OPT_FS|OPT_MOUNT, \
OPT_FS, \
OPT_BOOL(), \
BCH2_NO_SB_OPT, false, \
NULL, NULL) \