fs: add the ability for statmount() to report the sb_source

/proc/self/mountinfo displays the source for the mount, but statmount()
doesn't yet have a way to return it. Add a new STATMOUNT_SB_SOURCE flag,
claim the 32-bit __spare1 field to hold the offset into the str[] array.

Reviewed-by: Jan Kara <jack@suse.cz>
Signed-off-by: Jeff Layton <jlayton@kernel.org>
Link: https://lore.kernel.org/r/20241111-statmount-v4-3-2eaf35d07a80@kernel.org
Acked-by: Miklos Szeredi <mszeredi@redhat.com>
Signed-off-by: Christian Brauner <brauner@kernel.org>

diff --git a/fs/namespace.c b/fs/namespace.c
index dbd89fffd919be26e3570e3dbc46f120cacd96bb..d32b5afa99dcfb9176668bfe3e14a57264ce710e 100644 (file)
--- a/fs/namespace.c
+++ b/fs/namespace.c
@@ -5012,6 +5012,32 @@ static void statmount_fs_subtype(struct kstatmount *s, struct seq_file *seq)
                seq_puts(seq, sb->s_subtype);
 }
 
+static int statmount_sb_source(struct kstatmount *s, struct seq_file *seq)
+{
+       struct super_block *sb = s->mnt->mnt_sb;
+       struct mount *r = real_mount(s->mnt);
+
+       if (sb->s_op->show_devname) {
+               size_t start = seq->count;
+               int ret;
+
+               ret = sb->s_op->show_devname(seq, s->mnt->mnt_root);
+               if (ret)
+                       return ret;
+
+               if (unlikely(seq_has_overflowed(seq)))
+                       return -EAGAIN;
+
+               /* Unescape the result */
+               seq->buf[seq->count] = '\0';
+               seq->count = start;
+               seq_commit(seq, string_unescape_inplace(seq->buf + start, UNESCAPE_OCTAL));
+       } else if (r->mnt_devname) {
+               seq_puts(seq, r->mnt_devname);
+       }
+       return 0;
+}
+
 static void statmount_mnt_ns_id(struct kstatmount *s, struct mnt_namespace *ns)
 {
        s->sm.mask |= STATMOUNT_MNT_NS_ID;
@@ -5075,6 +5101,10 @@ static int statmount_string(struct kstatmount *s, u64 flag)
                sm->fs_subtype = start;
                statmount_fs_subtype(s, seq);
                break;
+       case STATMOUNT_SB_SOURCE:
+               sm->sb_source = start;
+               ret = statmount_sb_source(s, seq);
+               break;
        default:
                WARN_ON_ONCE(true);
                return -EINVAL;
@@ -5223,6 +5253,9 @@ static int do_statmount(struct kstatmount *s, u64 mnt_id, u64 mnt_ns_id,
        if (!err && s->mask & STATMOUNT_FS_SUBTYPE)
                err = statmount_string(s, STATMOUNT_FS_SUBTYPE);
 
+       if (!err && s->mask & STATMOUNT_SB_SOURCE)
+               err = statmount_string(s, STATMOUNT_SB_SOURCE);
+
        if (!err && s->mask & STATMOUNT_MNT_NS_ID)
                statmount_mnt_ns_id(s, ns);
 
@@ -5244,7 +5277,8 @@ 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_MNT_OPTS | STATMOUNT_FS_SUBTYPE)
+                             STATMOUNT_FS_TYPE | STATMOUNT_MNT_OPTS | \
+                             STATMOUNT_FS_SUBTYPE | STATMOUNT_SB_SOURCE)
 
 static int prepare_kstatmount(struct kstatmount *ks, struct mnt_id_req *kreq,
                              struct statmount __user *buf, size_t bufsize,

diff --git a/include/uapi/linux/mount.h b/include/uapi/linux/mount.h
index 2e939dddf9cbabe574dafdb6cff9ad4cf9298a74..2b49e9131d77165899d8e3c17366c6afaa8b7795 100644 (file)
--- a/include/uapi/linux/mount.h
+++ b/include/uapi/linux/mount.h
@@ -174,7 +174,7 @@ struct statmount {
        __u32 mnt_point;        /* [str] Mountpoint relative to current root */
        __u64 mnt_ns_id;        /* ID of the mount namespace */
        __u32 fs_subtype;       /* [str] Subtype of fs_type (if any) */
-       __u32 __spare1[1];
+       __u32 sb_source;        /* [str] Source string of the mount */
        __u64 __spare2[48];
        char str[];             /* Variable size part containing strings */
 };
@@ -210,6 +210,7 @@ struct mnt_id_req {
 #define STATMOUNT_MNT_NS_ID            0x00000040U     /* Want/got mnt_ns_id */
 #define STATMOUNT_MNT_OPTS             0x00000080U     /* Want/got mnt_opts */
 #define STATMOUNT_FS_SUBTYPE           0x00000100U     /* Want/got fs_subtype */
+#define STATMOUNT_SB_SOURCE            0x00000200U     /* Want/got sb_source */
 
 /*
  * Special @mnt_id values that can be passed to listmount