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

Josef Bacik <[email protected]> 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/[email protected]
Signed-off-by: Christian Brauner <[email protected]>

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,

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))

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

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;
@@ -561,14 +649,15 @@ 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();
  test_statmount_sb_basic();
  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");