libmount: implement X-mount.auto-fstypes

Fixes: #1969 Signed-off-by: Karel Zak <kzak@redhat.com>
util-linux · Jan 9, 2023 · 1592425 · poettering · Jan 9, 2023 · 1592425
1 parent 10dd071
commit 1592425
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diff --git a/libmount/src/context.c b/libmount/src/context.c
@@ -39,6 +39,7 @@
 #include "mountP.h"
 #include "strutils.h"
 #include "namespace.h"
+#include "match.h"
 
 #include <sys/wait.h>
 
@@ -1903,6 +1904,28 @@ int mnt_context_guess_srcpath_fstype(struct libmnt_context *cxt, char **type)
 	if (!mnt_context_switch_ns(cxt, ns_old))
 		return -MNT_ERR_NAMESPACE;
 
+	if (rc == 0 && *type) {
+		struct libmnt_optlist *ol = mnt_context_get_optlist(cxt);
+		struct libmnt_opt *opt;
+		const char *allowed;
+
+		if (!ol)
+			return -ENOMEM;
+
+		opt = mnt_optlist_get_named(ol,
+				"X-mount.auto-fstypes", cxt->map_userspace);
+
+		if (opt
+		    && (allowed = mnt_opt_get_value(opt))
+		    && !match_fstype(*type, allowed)) {
+			DBG(CXT, ul_debugobj(cxt, "%s is not allowd by auto-fstypes=%s",
+						*type, allowed));
+			free(*type);
+			*type = NULL;
+			rc = -MNT_ERR_NOFSTYPE;
+		}
+	}
+
 	return rc;
 }
 

diff --git a/libmount/src/context_mount.c b/libmount/src/context_mount.c
@@ -1484,7 +1484,7 @@ int mnt_context_get_mount_excode(
 			if (buf)
 				snprintf(buf, bufsz, restricted ?
 						_("failed to determine filesystem type") :
-						_("no filesystem type specified"));
+						_("no valid filesystem type specified"));
 			return MNT_EX_USAGE;
 		case -MNT_ERR_NOSOURCE:
 			if (uflags & MNT_MS_NOFAIL)

diff --git a/sys-utils/mount.8.adoc b/sys-utils/mount.8.adoc
@@ -630,6 +630,30 @@ The same as *X-** options, but stored permanently in user space. This means the
 +
 Note that before util-linux v2.30 the x-* options have not been maintained by libmount and stored in user space (functionality was the same as for X-* now), but due to the growing number of use-cases (in initrd, systemd etc.) the functionality has been extended to keep existing _fstab_ configurations usable without a change.
 
+*X-mount.auto-fstypes*=_list_::
+Specifies allowed or forbidden filesystem types for automatic filesystem
+detection.
++
+The _list_ is a comma-separated list of the filesystem names. The
+automatic filesystem detection is triggered by the "auto" filesystem type or
+when the filesystem type is not specified.
++
+Thy _list_ follows how mount
+evaluates type patterns (see *-t* for more details). Only specified filesystem
+types are allowed, or all specified types are forbidden if the list is prefixed
+by "no". 
++
+For example, X-mount.auto-fstypes="ext4,btrfs" accepts only ext4 and
+btrfs, and X-mount.auto-fstypes="novfat,xfs" accepts all filesystems except vfat
+and xfs.
++
+Note that comma is used as a separator between mount options, it means
+that auto-fstypes values have to be properly quoted, don’t forget that the shell
+strips off quotes and thus double quoting is required. For example:
+____
+mount -t auto -o'X-mount.auto-fstypes="noext2,ext3"'  /dev/sdc1 /mnt/test
+____
+
 *X-mount.mkdir*[=_mode_]::
 Allow to make a target directory (mountpoint) if it does not exist yet. The optional argument _mode_ specifies the filesystem access mode used for *mkdir*(2) in octal notation. The default mode is 0755. This functionality is supported only for root users or when *mount* is executed without suid permissions. The option is also supported as *x-mount.mkdir*, but this notation is deprecated since v2.30. See also *--mkdir* command line option.