Merge patch series "Add the ability to query mount options in statmount"

Josef Bacik <josef@toxicpanda.com> says:

Currently if you want to get mount options for a mount and you're using
statmount(), you still have to open /proc/mounts to parse the mount options.
statmount() does have the ability to store an arbitrary string however,
additionally the way we do that is with a seq_file, which is also how we use
->show_options for the individual file systems.

Extent statmount() to have a flag for fetching the mount options of a mount.
This allows users to not have to parse /proc mount for anything related to a
mount.  I've extended the existing statmount() test to validate this feature
works as expected.  As you can tell from the ridiculous amount of silly string
parsing, this is a huge win for users and climate change as we will no longer
have to waste several cycles parsing strings anymore.

Josef Bacik (4):
  fs: rename show_mnt_opts -> show_vfsmnt_opts
  fs: add a helper to show all the options for a mount
  fs: export mount options via statmount()
  sefltests: extend the statmount test for mount options

 fs/internal.h                                 |   5 +
 fs/namespace.c                                |   7 +
 fs/proc_namespace.c                           |  29 ++--
 include/uapi/linux/mount.h                    |   3 +-
 .../filesystems/statmount/statmount_test.c    | 131 +++++++++++++++++-
 5 files changed, 164 insertions(+), 11 deletions(-)

Link: https://lore.kernel.org/r/cover.1719257716.git.josef@toxicpanda.com
Signed-off-by: Christian Brauner <brauner@kernel.org>

4 files changed, 131 insertions, 6 deletions

diff --git a/fs/namespace.c b/fs/namespace.c
index a989e89b0a10..c53a0ee748c6 100644
--- a/fs/namespace.c
+++ b/fs/namespace.c
@@ -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,
diff --git a/fs/proc_namespace.c b/fs/proc_namespace.c
index 0a808951b7d3..e133b507ddf3 100644
--- a/fs/proc_namespace.c
+++ b/fs/proc_namespace.c
@@ -61,7 +61,7 @@ static int show_sb_opts(struct seq_file *m, struct super_block *sb)
 	return security_sb_show_options(m, sb);
 }
 
-static void show_mnt_opts(struct seq_file *m, struct vfsmount *mnt)
+static void show_vfsmnt_opts(struct seq_file *m, struct vfsmount *mnt)
 {
 	static const struct proc_fs_opts mnt_opts[] = {
 		{ MNT_NOSUID, ",nosuid" },
@@ -124,7 +124,7 @@ static int show_vfsmnt(struct seq_file *m, struct vfsmount *mnt)
 	err = show_sb_opts(m, sb);
 	if (err)
 		goto out;
-	show_mnt_opts(m, mnt);
+	show_vfsmnt_opts(m, mnt);
 	if (sb->s_op->show_options)
 		err = sb->s_op->show_options(m, mnt_path.dentry);
 	seq_puts(m, " 0 0\n");
@@ -153,7 +153,7 @@ static int show_mountinfo(struct seq_file *m, struct vfsmount *mnt)
 		goto out;
 
 	seq_puts(m, mnt->mnt_flags & MNT_READONLY ? " ro" : " rw");
-	show_mnt_opts(m, mnt);
+	show_vfsmnt_opts(m, mnt);
 
 	/* Tagged fields ("foo:X" or "bar") */
 	if (IS_MNT_SHARED(r))
diff --git a/include/uapi/linux/mount.h b/include/uapi/linux/mount.h
index ee1559cd6764..225bc366ffcb 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 __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
diff --git a/tools/testing/selftests/filesystems/statmount/statmount_test.c b/tools/testing/selftests/filesystems/statmount/statmount_test.c
index 4f7023c2de77..ece005864863 100644
--- a/tools/testing/selftests/filesystems/statmount/statmount_test.c
+++ b/tools/testing/selftests/filesystems/statmount/statmount_test.c
@@ -107,6 +107,7 @@ static char root_mntpoint[] = "/tmp/statmount_test_root.XXXXXX";
 static int orig_root;
 static uint64_t root_id, parent_id;
 static uint32_t old_root_id, old_parent_id;
+static FILE *f_mountinfo;
 
 static void cleanup_namespace(void)
 {
@@ -134,6 +135,11 @@ static void setup_namespace(void)
 	sprintf(buf, "0 %d 1", gid);
 	write_file("/proc/self/gid_map", buf);
 
+	f_mountinfo = fopen("/proc/self/mountinfo", "re");
+	if (!f_mountinfo)
+		ksft_exit_fail_msg("failed to open mountinfo: %s\n",
+				   strerror(errno));
+
 	ret = mount("", "/", NULL, MS_REC|MS_PRIVATE, NULL);
 	if (ret == -1)
 		ksft_exit_fail_msg("making mount tree private: %s\n",
@@ -435,6 +441,88 @@ static void test_statmount_fs_type(void)
 	free(sm);
 }
 
+static void test_statmount_mnt_opts(void)
+{
+	struct statmount *sm;
+	const char *statmount_opts;
+	char *line = NULL;
+	size_t len = 0;
+
+	sm = statmount_alloc(root_id, STATMOUNT_MNT_BASIC | STATMOUNT_MNT_OPTS,
+			     0);
+	if (!sm) {
+		ksft_test_result_fail("statmount mnt opts: %s\n",
+				      strerror(errno));
+		return;
+	}
+
+	while (getline(&line, &len, f_mountinfo) != -1) {
+		int i;
+		char *p, *p2;
+		unsigned int old_mnt_id;
+
+		old_mnt_id = atoi(line);
+		if (old_mnt_id != sm->mnt_id_old)
+			continue;
+
+		for (p = line, i = 0; p && i < 5; i++)
+			p = strchr(p + 1, ' ');
+		if (!p)
+			continue;
+
+		p2 = strchr(p + 1, ' ');
+		if (!p2)
+			continue;
+		*p2 = '\0';
+		p = strchr(p2 + 1, '-');
+		if (!p)
+			continue;
+		for (p++, i = 0; p && i < 2; i++)
+			p = strchr(p + 1, ' ');
+		if (!p)
+			continue;
+		p++;
+
+		/* skip generic superblock options */
+		if (strncmp(p, "ro", 2) == 0)
+			p += 2;
+		else if (strncmp(p, "rw", 2) == 0)
+			p += 2;
+		if (*p == ',')
+			p++;
+		if (strncmp(p, "sync", 4) == 0)
+			p += 4;
+		if (*p == ',')
+			p++;
+		if (strncmp(p, "dirsync", 7) == 0)
+			p += 7;
+		if (*p == ',')
+			p++;
+		if (strncmp(p, "lazytime", 8) == 0)
+			p += 8;
+		if (*p == ',')
+			p++;
+		p2 = strrchr(p, '\n');
+		if (p2)
+			*p2 = '\0';
+
+		statmount_opts = sm->str + sm->mnt_opts;
+		if (strcmp(statmount_opts, p) != 0)
+			ksft_test_result_fail(
+				"unexpected mount options: '%s' != '%s'\n",
+				statmount_opts, p);
+		else
+			ksft_test_result_pass("statmount mount options\n");
+		free(sm);
+		free(line);
+		return;
+	}
+
+	ksft_test_result_fail("didnt't find mount entry\n");
+	free(sm);
+	free(line);
+}
+
 static void test_statmount_string(uint64_t mask, size_t off, const char *name)
 {
 	struct statmount *sm;
@@ -561,7 +649,7 @@ int main(void)
 
 	setup_namespace();
 
-	ksft_set_plan(14);
+	ksft_set_plan(15);
 	test_listmount_empty_root();
 	test_statmount_zero_mask();
 	test_statmount_mnt_basic();
@@ -569,6 +657,7 @@ int main(void)
 	test_statmount_mnt_root();
 	test_statmount_mnt_point();
 	test_statmount_fs_type();
+	test_statmount_mnt_opts();
 	test_statmount_string(STATMOUNT_MNT_ROOT, str_off(mnt_root), "mount root");
 	test_statmount_string(STATMOUNT_MNT_POINT, str_off(mnt_point), "mount point");
 	test_statmount_string(STATMOUNT_FS_TYPE, str_off(fs_type), "fs type");