libmount: support MS_RDONLY on write-protected devices

This feature is supported by mount(8) only. It seems better move
this code to libmount. The results is more simple mount(8) and the
feature is accessible for all libmount users.

Signed-off-by: Karel Zak <kzak@redhat.com>

1 files changed, 27 insertions, 0 deletions

diff --git a/libmount/src/context_mount.c b/libmount/src/context_mount.c
index 6368e9ba8..1c8a62924 100644
--- a/libmount/src/context_mount.c
+++ b/libmount/src/context_mount.c
@@ -1083,6 +1083,7 @@ int mnt_context_mount(struct libmnt_context *cxt)
 	assert(cxt->helper_exec_status == 1);
 	assert(cxt->syscall_status == 1);
 
+again:
 	rc = mnt_context_prepare_mount(cxt);
 	if (!rc)
 		rc = mnt_context_prepare_update(cxt);
@@ -1090,6 +1091,32 @@ int mnt_context_mount(struct libmnt_context *cxt)
 		rc = mnt_context_do_mount(cxt);
 	if (!rc)
 		rc = mnt_context_update_tabs(cxt);
+
+	/*
+	 * Read-only device; try mount filesystem read-only
+	 */
+	if ((rc == -EROFS && !mnt_context_syscall_called(cxt))	/* before syscall; rdonly loopdev */
+	     || mnt_context_get_syscall_errno(cxt) == EROFS	/* syscall failed with EROFS */
+	     || mnt_context_get_syscall_errno(cxt) == EACCES)	/* syscall failed with EACCES */
+	{
+		unsigned long mflags = 0;
+
+		mnt_context_get_mflags(cxt, &mflags);
+
+		if (!(mflags & MS_RDONLY)			/* not yet RDONLY */
+		    && !(mflags & MS_REMOUNT)			/* not remount */
+		    && !(mflags & MS_BIND)			/* not bin mount */
+		    && !mnt_context_is_rwonly_mount(cxt)) {	/* no explicit read-write */
+
+			assert(!(cxt->flags & MNT_FL_FORCED_RDONLY));
+			DBG(CXT, ul_debugobj(cxt, "write-protected source, trying RDONLY."));
+
+			mnt_context_reset_status(cxt);
+			mnt_context_set_mflags(cxt, mflags | MS_RDONLY);
+			cxt->flags |= MNT_FL_FORCED_RDONLY;
+			goto again;
+		}
+	}
 	return rc;
 }