From 2f4d4503e9e5ab765a7948f98bc5deef7850f607 Mon Sep 17 00:00:00 2001
From: Miklos Szeredi <mszeredi@redhat.com>
Date: Tue, 12 Nov 2024 11:10:04 +0100
Subject: [PATCH] statmount: add flag to retrieve unescaped options
Filesystem options can be retrieved with STATMOUNT_MNT_OPTS, which
returns a string of comma separated options, where some characters are
escaped using the \OOO notation.
Add a new flag, STATMOUNT_OPT_ARRAY, which instead returns the raw
option values separated with '\0' charaters.
Since escaped charaters are rare, this inteface is preferable for
non-libmount users which likley don't want to deal with option
de-escaping.
Example code:
if (st->mask & STATMOUNT_OPT_ARRAY) {
const char *opt = st->str + st->opt_array;
for (unsigned int i = 0; i < st->opt_num; i++) {
printf("opt_array[%i]: <%s>\n", i, opt);
opt += strlen(opt) + 1;
}
}
Example ouput:
(1) mnt_opts: <lowerdir+=/l\054w\054r,lowerdir+=/l\054w\054r1,upperdir=/upp\054r,workdir=/w\054rk,redirect_dir=nofollow,uuid=null>
(2) opt_array[0]: <lowerdir+=/l,w,r>
opt_array[1]: <lowerdir+=/l,w,r1>
opt_array[2]: <upperdir=/upp,r>
opt_array[3]: <workdir=/w,rk>
opt_array[4]: <redirect_dir=nofollow>
opt_array[5]: <uuid=null>
Signed-off-by: Miklos Szeredi <mszeredi@redhat.com>
Link: https://lore.kernel.org/r/20241112101006.30715-1-mszeredi@redhat.com
Acked-by: Jeff Layton <jlayton@kernel.org>
[brauner: tweak variable naming and parsing add example output]
Signed-off-by: Christian Brauner <brauner@kernel.org>
---
fs/namespace.c | 47 +++++++++++++++++++++++++++++++++++++-
include/uapi/linux/mount.h | 7 ++++--
2 files changed, 51 insertions(+), 3 deletions(-)
diff --git a/fs/namespace.c b/fs/namespace.c
index d32b5afa99dcf..4f39c4aba85dd 100644
--- a/fs/namespace.c
+++ b/fs/namespace.c
@@ -5072,6 +5072,43 @@ static int statmount_mnt_opts(struct kstatmount *s, struct seq_file *seq)
return 0;
}
+static int statmount_opt_array(struct kstatmount *s, struct seq_file *seq)
+{
+ struct vfsmount *mnt = s->mnt;
+ struct super_block *sb = mnt->mnt_sb;
+ size_t start = seq->count;
+ char *buf_start, *buf_end, *opt_start, *opt_end;
+ u32 count = 0;
+ int err;
+
+ if (!sb->s_op->show_options)
+ return 0;
+
+ buf_start = seq->buf + start;
+ 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;
+
+ buf_end = seq->buf + seq->count;
+ *buf_end = '\0';
+ for (opt_start = buf_start + 1; opt_start < buf_end; opt_start = opt_end + 1) {
+ opt_end = strchrnul(opt_start, ',');
+ *opt_end = '\0';
+ buf_start += string_unescape(opt_start, buf_start, 0, UNESCAPE_OCTAL) + 1;
+ if (WARN_ON_ONCE(++count == 0))
+ return -EOVERFLOW;
+ }
+ seq->count = buf_start - 1 - seq->buf;
+ s->sm.opt_num = count;
+ return 0;
+}
+
static int statmount_string(struct kstatmount *s, u64 flag)
{
int ret = 0;
@@ -5097,6 +5134,10 @@ static int statmount_string(struct kstatmount *s, u64 flag)
sm->mnt_opts = start;
ret = statmount_mnt_opts(s, seq);
break;
+ case STATMOUNT_OPT_ARRAY:
+ sm->opt_array = start;
+ ret = statmount_opt_array(s, seq);
+ break;
case STATMOUNT_FS_SUBTYPE:
sm->fs_subtype = start;
statmount_fs_subtype(s, seq);
@@ -5250,6 +5291,9 @@ static int do_statmount(struct kstatmount *s, u64 mnt_id, u64 mnt_ns_id,
if (!err && s->mask & STATMOUNT_MNT_OPTS)
err = statmount_string(s, STATMOUNT_MNT_OPTS);
+ if (!err && s->mask & STATMOUNT_OPT_ARRAY)
+ err = statmount_string(s, STATMOUNT_OPT_ARRAY);
+
if (!err && s->mask & STATMOUNT_FS_SUBTYPE)
err = statmount_string(s, STATMOUNT_FS_SUBTYPE);
@@ -5278,7 +5322,8 @@ 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_SB_SOURCE)
+ STATMOUNT_FS_SUBTYPE | STATMOUNT_SB_SOURCE | \
+ STATMOUNT_OPT_ARRAY)
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 2b49e9131d771..c0fda4604187d 100644
--- a/include/uapi/linux/mount.h
+++ b/include/uapi/linux/mount.h
@@ -154,7 +154,7 @@ struct mount_attr {
*/
struct statmount {
__u32 size; /* Total size, including strings */
- __u32 mnt_opts; /* [str] Mount options of the mount */
+ __u32 mnt_opts; /* [str] Options (comma separated, escaped) */
__u64 mask; /* What results were written */
__u32 sb_dev_major; /* Device ID */
__u32 sb_dev_minor;
@@ -175,7 +175,9 @@ struct statmount {
__u64 mnt_ns_id; /* ID of the mount namespace */
__u32 fs_subtype; /* [str] Subtype of fs_type (if any) */
__u32 sb_source; /* [str] Source string of the mount */
- __u64 __spare2[48];
+ __u32 opt_num; /* Number of fs options */
+ __u32 opt_array; /* [str] Array of nul terminated fs options */
+ __u64 __spare2[47];
char str[]; /* Variable size part containing strings */
};
@@ -211,6 +213,7 @@ struct mnt_id_req {
#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 */
+#define STATMOUNT_OPT_ARRAY 0x00000400U /* Want/got opt_... */
/*
* Special @mnt_id values that can be passed to listmount