mountpoint: use statmount() syscall on modern kernels

Improve mountpoint(1) to use the modern statmount() system call
(available since Linux 6.8) instead of parsing /proc/self/mountinfo.

- Works without /proc mounted on modern kernels
- More efficient than parsing /proc/self/mountinfo
- Better detection of bind mounts via statmount()
- Graceful fallback maintains compatibility

Addresses: https://github.com/util-linux/util-linux/issues/3806
Signed-off-by: Karel Zak <kzak@redhat.com>

diff --git a/sys-utils/mountpoint.1.adoc b/sys-utils/mountpoint.1.adoc
index bc8a2e9ed69b8f1e02333af9cc31fa316a65fc3a..0e1252c72c91769910936caef461497f32a6827f 100644 (file)
--- a/sys-utils/mountpoint.1.adoc
+++ b/sys-utils/mountpoint.1.adoc
@@ -18,7 +18,7 @@ mountpoint - see if a directory or file is a mountpoint
 
 == DESCRIPTION
 
-*mountpoint* checks whether the given _directory_ or _file_ is mentioned in the _/proc/self/mountinfo_ file.
+*mountpoint* checks whether the given _directory_ or _file_ is a mountpoint. On kernels that support the *statmount*(2) system call (Linux 6.8 and newer), it uses that interface. On older kernels, it falls back to reading _/proc/self/mountinfo_.
 
 == OPTIONS
 

diff --git a/sys-utils/mountpoint.c b/sys-utils/mountpoint.c
index 6294a4c07a8971934008e6ee7d44e59d96f22f55..8a114b5bb068f76026d64e78048dba4af6e278f0 100644 (file)
--- a/sys-utils/mountpoint.c
+++ b/sys-utils/mountpoint.c
@@ -31,6 +31,7 @@
 #include "c.h"
 #include "closestream.h"
 #include "pathnames.h"
+#include "mount-api-utils.h"
 
 #define MOUNTPOINT_EXIT_NOMNT  32
 
@@ -44,13 +45,80 @@ struct mountpoint_control {
                quiet;
 };
 
+#ifdef HAVE_STATMOUNT_API
+/*
+ * dir_to_device_statmount - check if path is a mountpoint using statmount()
+ * @ctl: mountpoint control structure
+ *
+ * Returns: <0 on error, 0 if mountpoint, 1 if not a mountpoint
+ */
+static int dir_to_device_statmount(struct mountpoint_control *ctl)
+{
+       struct libmnt_fs *fs = NULL;
+       const char *mnt_target;
+       char *cn = NULL;
+       uint64_t id = 0;
+       int rc;
+
+       cn = mnt_resolve_path(ctl->path, NULL);
+
+       rc = mnt_id_from_path(cn ? cn : ctl->path, &id, NULL);
+       if (rc)
+               goto done;
+
+       fs = mnt_new_fs();
+       if (!fs) {
+               rc = -ENOMEM;
+               goto done;
+       }
+
+       mnt_fs_set_uniq_id(fs, id);
+
+       rc = mnt_fs_fetch_statmount(fs, STATMOUNT_MNT_POINT | STATMOUNT_SB_BASIC);
+       if (rc)
+               goto done;
+
+       mnt_target = mnt_fs_get_target(fs);
+       if (!mnt_target) {
+               rc = -EINVAL;
+               goto done;
+       }
+
+       if (strcmp(mnt_target, cn ? cn : ctl->path) != 0)
+               rc = 1; /* not a mountpoint */
+       else {
+               ctl->dev = mnt_fs_get_devno(fs);
+               rc = 0; /* is a mountpoint */
+       }
+done:
+       free(cn);
+       mnt_unref_fs(fs);
+       return rc;
+}
+#endif /* STATMOUNT_MNT_POINT */
+
+/*
+ * dir_to_device - check if path is a mountpoint
+ * @ctl: mountpoint control structure
+ *
+ * Returns: <0 on error, 0 if mountpoint, 1 if not a mountpoint
+ */
 static int dir_to_device(struct mountpoint_control *ctl)
 {
-       struct libmnt_table *tb = mnt_new_table_from_file(_PATH_PROC_MOUNTINFO);
+       struct libmnt_table *tb;
        struct libmnt_fs *fs;
        struct libmnt_cache *cache;
-       int rc = -1;
+       int rc;
 
+#ifdef HAVE_STATMOUNT_API
+       rc = dir_to_device_statmount(ctl);
+       if (rc >= 0)
+               return rc;
+#endif
+       /*
+        * Fallback for older kernels without statmount() support
+        */
+       tb = mnt_new_table_from_file(_PATH_PROC_MOUNTINFO);
        if (!tb) {
                /*
                 * Fallback. Traditional way to detect mountpoints. This way
@@ -66,16 +134,18 @@ static int dir_to_device(struct mountpoint_control *ctl)
                free(cn);
 
                if (len < 0 || (size_t) len >= sizeof(buf))
-                       return -1;
-               if (stat(buf, &pst) !=0)
-                       return -1;
+                       return -EINVAL;
+
+               rc = stat(buf, &pst);
+               if (rc)
+                       return -errno;
 
                if (ctl->st.st_dev != pst.st_dev || ctl->st.st_ino == pst.st_ino) {
                        ctl->dev = ctl->st.st_dev;
-                       return 0;
+                       return 0;       /* is a mountpoint */
                }
 
-               return -1;
+               return 1;       /* not a mountpoint */
        }
 
        /* to canonicalize all necessary paths */
@@ -86,8 +156,9 @@ static int dir_to_device(struct mountpoint_control *ctl)
        fs = mnt_table_find_target(tb, ctl->path, MNT_ITER_BACKWARD);
        if (fs && mnt_fs_get_target(fs)) {
                ctl->dev = mnt_fs_get_devno(fs);
-               rc = 0;
-       }
+               rc = 0; /* is a mountpoint */
+       } else
+               rc = 1; /* not a mountpoint */
 
        mnt_unref_table(tb);
        return rc;
@@ -129,7 +200,7 @@ static void __attribute__((__noreturn__)) usage(void)
 
 int main(int argc, char **argv)
 {
-       int c;
+       int c, rc;
        struct mountpoint_control ctl = { NULL };
 
        enum {
@@ -196,11 +267,26 @@ int main(int argc, char **argv)
        if (ctl.dev_devno)
                return print_devno(&ctl) ? MOUNTPOINT_EXIT_NOMNT : EXIT_SUCCESS;
 
-       if ((ctl.nofollow && S_ISLNK(ctl.st.st_mode)) || dir_to_device(&ctl)) {
+       if (ctl.nofollow && S_ISLNK(ctl.st.st_mode)) {
+               if (!ctl.quiet)
+                       printf(_("%s is not a mountpoint\n"), ctl.path);
+               return MOUNTPOINT_EXIT_NOMNT;
+       }
+
+       rc = dir_to_device(&ctl);
+       if (rc < 0) {
+               if (!ctl.quiet) {
+                       errno = -rc;
+                       warn("%s", ctl.path);
+               }
+               return EXIT_FAILURE;
+       }
+       if (rc == 1) {
                if (!ctl.quiet)
                        printf(_("%s is not a mountpoint\n"), ctl.path);
                return MOUNTPOINT_EXIT_NOMNT;
        }
+
        if (ctl.fs_devno)
                printf("%u:%u\n", major(ctl.dev), minor(ctl.dev));
        else if (!ctl.quiet)