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fs: export mount options via statmount()

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statmount() can export arbitrary strings, so utilize the __spare1 slot
for a mnt_opts string pointer, and then support asking for and setting
the mount options during statmount().  This calls into the helper for
showing mount options, which already uses a seq_file, so fits in nicely
with our existing mechanism for exporting strings via statmount().

Signed-off-by: Josef Bacik <josef@toxicpanda.com>
Link: https://lore.kernel.org/r/3aa6bf8bd5d0a21df9ebd63813af8ab532c18276.1719257716.git.josef@toxicpanda.com
Reviewed-by: Jeff Layton <jlayton@kernel.org>
[brauner: only call sb->s_op->show_options()]
Signed-off-by: Christian Brauner <brauner@kernel.org>
This commit is contained in:
Josef Bacik 2024-06-24 15:40:52 -04:00 committed by Christian Brauner
parent c72b6b7224
commit f9af549d1f
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GPG key ID: 91C61BC06578DCA2
2 changed files with 38 additions and 2 deletions
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37
fs/namespace.c
View file

@ -4980,6 +4980,34 @@ static void statmount_mnt_ns_id(struct kstatmount *s, struct mnt_namespace *ns)
s->sm.mnt_ns_id = ns->seq;
}
static int statmount_mnt_opts(struct kstatmount *s, struct seq_file *seq)
{
struct vfsmount *mnt = s->mnt;
struct super_block *sb = mnt->mnt_sb;
int err;
if (sb->s_op->show_options) {
size_t start = seq->count;
err = sb->s_op->show_options(seq, mnt->mnt_root);
if (err)
return err;
if (unlikely(seq_has_overflowed(seq)))
return -EAGAIN;
if (seq->count == start)
return 0;
/* skip leading comma */
memmove(seq->buf + start, seq->buf + start + 1,
seq->count - start - 1);
seq->count--;
}
return 0;
}
static int statmount_string(struct kstatmount *s, u64 flag)
{
int ret;
@ -5000,6 +5028,10 @@ static int statmount_string(struct kstatmount *s, u64 flag)
sm->mnt_point = seq->count;
ret = statmount_mnt_point(s, seq);
break;
case STATMOUNT_MNT_OPTS:
sm->mnt_opts = seq->count;
ret = statmount_mnt_opts(s, seq);
break;
default:
WARN_ON_ONCE(true);
return -EINVAL;
@ -5130,6 +5162,9 @@ static int do_statmount(struct kstatmount *s, u64 mnt_id, u64 mnt_ns_id,
if (!err && s->mask & STATMOUNT_MNT_POINT)
err = statmount_string(s, STATMOUNT_MNT_POINT);
if (!err && s->mask & STATMOUNT_MNT_OPTS)
err = statmount_string(s, STATMOUNT_MNT_OPTS);
if (!err && s->mask & STATMOUNT_MNT_NS_ID)
statmount_mnt_ns_id(s, ns);
@ -5151,7 +5186,7 @@ static inline bool retry_statmount(const long ret, size_t *seq_size)
}
#define STATMOUNT_STRING_REQ (STATMOUNT_MNT_ROOT | STATMOUNT_MNT_POINT | \
STATMOUNT_FS_TYPE)
STATMOUNT_FS_TYPE | STATMOUNT_MNT_OPTS)
static int prepare_kstatmount(struct kstatmount *ks, struct mnt_id_req *kreq,
struct statmount __user *buf, size_t bufsize,

3
include/uapi/linux/mount.h
View file

@ -154,7 +154,7 @@ struct mount_attr {
*/
struct statmount {
__u32 size; /* Total size, including strings */
__u32 __spare1;
__u32 mnt_opts; /* [str] Mount options of the mount */
__u64 mask; /* What results were written */
__u32 sb_dev_major; /* Device ID */
__u32 sb_dev_minor;
@ -206,6 +206,7 @@ struct mnt_id_req {
#define STATMOUNT_MNT_POINT 0x00000010U /* Want/got mnt_point */
#define STATMOUNT_FS_TYPE 0x00000020U /* Want/got fs_type */
#define STATMOUNT_MNT_NS_ID 0x00000040U /* Want/got mnt_ns_id */
#define STATMOUNT_MNT_OPTS 0x00000080U /* Want/got mnt_opts */
/*
* Special @mnt_id values that can be passed to listmount