[PATCH] statmount: add flag to retrieve unescaped options

[Miklos Szeredi <mszeredi@redhat.com>]

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;
		}
	}

Signed-off-by: Miklos Szeredi <mszeredi@redhat.com>
---
 fs/namespace.c             | 42 ++++++++++++++++++++++++++++++++++++++
 include/uapi/linux/mount.h |  7 +++++--
 2 files changed, 47 insertions(+), 2 deletions(-)

diff --git a/fs/namespace.c b/fs/namespace.c
index 9a4ab1bc8b94..a16f75011610 100644
--- a/fs/namespace.c
+++ b/fs/namespace.c
@@ -5074,6 +5074,41 @@ 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;
+	u32 count = 0;
+	char *p, *end, *next, *u = seq->buf + start;
+	int err;
+
+       if (!sb->s_op->show_options)
+               return 0;
+
+       err = sb->s_op->show_options(seq, mnt->mnt_root);
+       if (err)
+	       return err;
+
+       if (unlikely(seq_has_overflowed(seq)))
+	       return -EAGAIN;
+
+       end = seq->buf + seq->count;
+       *end = '\0';
+       for (p = u + 1; p < end; p = next + 1) {
+               next = strchrnul(p, ',');
+               *next = '\0';
+               u += string_unescape(p, u, 0, UNESCAPE_OCTAL) + 1;
+	       count++;
+	       if (!count)
+		       return -EOVERFLOW;
+       }
+       seq->count = u - 1 - seq->buf;
+       s->sm.opt_num = count;
+
+       return 0;
+}
+
 static int statmount_string(struct kstatmount *s, u64 flag)
 {
 	int ret = 0;
@@ -5099,6 +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);
@@ -5252,6 +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);
 
diff --git a/include/uapi/linux/mount.h b/include/uapi/linux/mount.h
index 2b49e9131d77..c0fda4604187 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
-- 
2.47.0