libmount: add support for MS_REMOUNT on --all

This patch add to support for remount-all operation to
libmount and mount(8).

For example:
	mount --all -o remount,ro -t vfat

to remount read-only all VFAT filesystems.

Addresses: https://github.com/karelzak/util-linux/issues/589
Signed-off-by: Karel Zak <kzak@redhat.com>

Documentation/TODO

@@ -65,11 +65,6 @@ bash completion
 libmount (mount/umount)
 -----------------------
 
- - remount all filesystems given their type, for example:
-        mount -a -t tmpfs -o remount
-   It should be probably enough to add remount_all() to mount(8) in way we
-   already have mount_all().  https://github.com/karelzak/util-linux/issues/589
-
  - add --onlyonce to force mount(8) to check if mountpoint is already used. Now
    "already mounted" detection is used for --all only. The problem is if you
    call "mount <mountpoint>" more than once for in fstab defined tmpfs (or network

libmount/docs/libmount-sections.txt

@@ -135,6 +135,7 @@ mnt_context_do_mount
 mnt_context_finalize_mount
 mnt_context_mount
 mnt_context_next_mount
+mnt_context_next_remount
 mnt_context_prepare_mount
 <SUBSECTION>
 MNT_MS_COMMENT

libmount/src/context.c

@@ -193,6 +193,49 @@ int mnt_reset_context(struct libmnt_context *cxt)
 	return 0;
 }
 
+struct libmnt_context *mnt_copy_context(struct libmnt_context *o)
+{
+	struct libmnt_context *n;
+
+	n = mnt_new_context();
+	if (!n)
+		return NULL;
+
+	DBG(CXT, ul_debugobj(n, "<---- clone ---->"));
+
+	n->flags = o->flags;
+
+	if (o->fs) {
+		n->fs = mnt_copy_fs(NULL, o->fs);
+		if (!n->fs)
+			goto failed;
+	}
+
+	n->mtab = o->mtab;
+	mnt_ref_table(n->mtab);
+
+	n->mtab = o->utab;
+	mnt_ref_table(n->utab);
+
+	if (o->helper)
+		n->helper = strdup(o->helper);
+	if (o->orig_user)
+		n->orig_user = strdup(o->orig_user);
+
+	n->mountflags = o->mountflags;
+	n->mountdata = o->mountdata;
+
+	mnt_context_reset_status(n);
+
+	n->table_fltrcb = o->table_fltrcb;
+	n->table_fltrcb_data = o->table_fltrcb_data;
+
+	return n;
+failed:
+	mnt_free_context(n);
+	return NULL;
+}
+
 /**
  * mnt_context_reset_status:
  * @cxt: context

libmount/src/context_mount.c

@@ -1382,6 +1382,112 @@ int mnt_context_next_mount(struct libmnt_context *cxt,
 	return 0;
 }
 
+
+/**
+ * mnt_context_next_remount:
+ * @cxt: context
+ * @itr: iterator
+ * @fs: returns the current filesystem
+ * @mntrc: returns the return code from mnt_context_mount()
+ * @ignored: returns 1 for non-matching
+ *
+ * This function tries to remount the next mounted filesystem (as returned by
+ * mnt_context_get_mtab()).
+ *
+ * You can filter out filesystems by:
+ *	mnt_context_set_options_pattern() to simulate mount -a -O pattern
+ *	mnt_context_set_fstype_pattern()  to simulate mount -a -t pattern
+ *
+ * If the filesystem does not match defined criteria, then the
+ * mnt_context_next_remount() function returns zero, but the @ignored is
+ * non-zero.
+ *
+ * If mount(2) syscall or mount.type helper failed, then the
+ * mnt_context_renext_mount() function returns zero, but the @mntrc is non-zero.
+ * Use also mnt_context_get_status() to check if the filesystem was
+ * successfully mounted.
+ *
+ * See mnt_context_mount() for more details about errors and warnings.
+ *
+ * Returns: 0 on success,
+ *         <0 in case of error (!= mount(2) errors)
+ *          1 at the end of the list.
+ */
+int mnt_context_next_remount(struct libmnt_context *cxt,
+			   struct libmnt_iter *itr,
+			   struct libmnt_fs **fs,
+			   int *mntrc,
+			   int *ignored)
+{
+	struct libmnt_context *remount_cxt = NULL;
+	struct libmnt_table *mtab;
+	const char *tgt;
+	int rc;
+
+	if (ignored)
+		*ignored = 0;
+	if (mntrc)
+		*mntrc = 0;
+
+	if (!cxt || !fs || !itr)
+		return -EINVAL;
+
+	rc = mnt_context_get_mtab(cxt, &mtab);
+	if (rc)
+		return rc;
+
+	rc = mnt_table_next_fs(mtab, itr, fs);
+	if (rc != 0)
+		return rc;	/* more filesystems (or error) */
+
+	tgt = mnt_fs_get_target(*fs);
+
+	DBG(CXT, ul_debugobj(cxt, "next-remount: trying %s", tgt));
+
+	/* ignore filesystems which don't match options patterns */
+	if ((cxt->fstype_pattern && !mnt_fs_match_fstype(*fs,
+					cxt->fstype_pattern)) ||
+
+	/* ignore filesystems which don't match type patterns */
+	   (cxt->optstr_pattern && !mnt_fs_match_options(*fs,
+					cxt->optstr_pattern))) {
+		if (ignored)
+			*ignored = 1;
+		DBG(CXT, ul_debugobj(cxt, "next-remount: not-match "
+				"[fstype: %s, t-pattern: %s, options: %s, O-pattern: %s]",
+				mnt_fs_get_fstype(*fs),
+				cxt->fstype_pattern,
+				mnt_fs_get_options(*fs),
+				cxt->optstr_pattern));
+		return 0;
+	}
+
+	/* make sure fstab is already read to avoid fstab parsing in cloned context */
+	mnt_context_get_fstab(cxt, NULL);
+
+	/* clone context */
+	remount_cxt = mnt_copy_context(cxt);
+	if (!remount_cxt)
+		return -ENOMEM;
+
+	rc = mnt_context_set_target(remount_cxt, tgt);
+	if (!rc) {
+		/*
+		 * "-t <pattern>" is used to filter out fstab entries, but for ordinary
+		 * mount operation -t means "-t <type>". We have to zeroize the pattern
+		 * to avoid misinterpretation.
+		 */
+		remount_cxt->fstype_pattern = NULL;
+		rc = mnt_context_mount(remount_cxt);
+
+		if (mntrc)
+			*mntrc = rc;
+	}
+
+	mnt_free_context(remount_cxt);
+	return 0;
+}
+
 /*
  * Returns 1 if @dir parent is shared
  */

libmount/src/libmount.h.in

@@ -849,6 +849,12 @@ extern int mnt_context_next_mount(struct libmnt_context *cxt,
 				struct libmnt_fs **fs,
 				int *mntrc, int *ignored);
 
+extern int mnt_context_next_remount(struct libmnt_context *cxt,
+                           struct libmnt_iter *itr,
+                           struct libmnt_fs **fs,
+                           int *mntrc,
+                           int *ignored);
+
 extern int mnt_context_prepare_mount(struct libmnt_context *cxt)
 			__ul_attribute__((warn_unused_result));
 extern int mnt_context_do_mount(struct libmnt_context *cxt);

libmount/src/libmount.sym

@@ -344,4 +344,5 @@ MOUNT_2.33 {
 
 MOUNT_2.34 {
 	mnt_guess_system_root;
+	mnt_context_next_remount;
 } MOUNT_2.33;

libmount/src/mountP.h

@@ -403,6 +403,7 @@ extern int __mnt_fs_set_fstype_ptr(struct libmnt_fs *fs, char *fstype)
 			__attribute__((nonnull(1)));
 
 /* context.c */
+extern struct libmnt_context *mnt_copy_context(struct libmnt_context *o);
 extern int mnt_context_mtab_writable(struct libmnt_context *cxt);
 extern int mnt_context_utab_writable(struct libmnt_context *cxt);
 extern const char *mnt_context_get_writable_tabpath(struct libmnt_context *cxt);

sys-utils/mount.8

@@ -580,6 +580,10 @@ mount or btrfs) to detect already mounted filesystems. The kernel table with
 already mounted filesystems is cached during \fBmount \-\-all\fR. It means
 that all duplicated fstab entries will be mounted.
 .sp
+The option \fB\-\-all\fR is possible to use for remount operation too. In this
+case all filters (\fB\-t\fR and \fB\-O\fR) are applied to the table of already
+mounted filesystems.
+.sp
 Note that it is a bad practice to use \fBmount \-a\fR for
 .I fstab
 checking. The recommended solution is \fBfindmnt \-\-verify\fR.

sys-utils/mount.c

@@ -231,6 +231,57 @@ static int mount_all(struct libmnt_context *cxt)
 	return rc;
 }
 
+
+/*
+ * mount -a -o remount
+ */
+static int remount_all(struct libmnt_context *cxt)
+{
+	struct libmnt_iter *itr;
+	struct libmnt_fs *fs;
+	int mntrc, ignored, rc = MNT_EX_SUCCESS;
+
+	int nsucc = 0, nerrs = 0;
+
+	itr = mnt_new_iter(MNT_ITER_FORWARD);
+	if (!itr) {
+		warn(_("failed to initialize libmount iterator"));
+		return MNT_EX_SYSERR;
+	}
+
+	while (mnt_context_next_remount(cxt, itr, &fs, &mntrc, &ignored) == 0) {
+
+		const char *tgt = mnt_fs_get_target(fs);
+
+		if (ignored) {
+			if (mnt_context_is_verbose(cxt))
+				printf(_("%-25s: ignored\n"), tgt);
+		} else {
+			if (mk_exit_code(cxt, mntrc) == MNT_EX_SUCCESS) {
+				nsucc++;
+
+				/* Note that MNT_EX_SUCCESS return code does
+				 * not mean that FS has been really mounted
+				 * (e.g. nofail option) */
+				if (mnt_context_get_status(cxt)
+				    && mnt_context_is_verbose(cxt))
+					printf("%-25s: successfully remounted\n", tgt);
+			} else
+				nerrs++;
+		}
+	}
+
+	if (nerrs == 0)
+		rc = MNT_EX_SUCCESS;		/* all success */
+	else if (nsucc == 0)
+		rc = MNT_EX_FAIL;		/* all failed */
+	else
+		rc = MNT_EX_SOMEOK;		/* some success, some failed */
+
+	mnt_free_iter(itr);
+	return rc;
+}
+
 static void success_message(struct libmnt_context *cxt)
 {
 	unsigned long mflags = 0;
@@ -836,7 +887,10 @@ int main(int argc, char **argv)
 		/*
 		 * A) Mount all
 		 */
-		rc = mount_all(cxt);
+		if (has_remount_flag(cxt))
+			rc = remount_all(cxt);
+		else
+			rc = mount_all(cxt);
 		goto done;
 
 	} else if (argc == 0 && (mnt_context_get_source(cxt) ||