From: Karel Zak <kzak@redhat.com>
Date: Tue, 25 Apr 2023 14:25:14 +0000 (+0200)
Subject: libmount: improve ENOSYS fallback
X-Git-Tag: v2.39~56
X-Git-Url: http://git.ipfire.org/?a=commitdiff_plain;h=009b369c7d95e811470eb5d626b9b498539a007a;p=thirdparty%2Futil-linux.git

libmount: improve ENOSYS fallback

In some cases, for example:

 # mount -t foo,bar,ext4 /dev/sdc /mnt/test

libmount calls fsopen() later (after mount preparation stage), but we
need during preparation check if hook_mount.c stuff (new API) is usable.

Let's do it by dummy fsopen() call.

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

diff --git a/libmount/src/hook_mount.c b/libmount/src/hook_mount.c
index 2dbe5217cc..9d1ffaf0d1 100644
--- a/libmount/src/hook_mount.c
+++ b/libmount/src/hook_mount.c
@@ -496,6 +496,20 @@ static int hook_attach_target(struct libmnt_context *cxt,
 	return rc == 0 ? 0 : -errno;
 }
 
+static inline int fsopen_is_supported(void)
+{
+	int dummy, rc = 1;
+
+	errno = 0;
+	dummy = fsopen(NULL, FSOPEN_CLOEXEC);
+
+	if (errno == ENOSYS)
+		rc = 0;
+	if (dummy >= 0)
+		close(dummy);
+	return rc;
+}
+
 /*
  * open_tree() and fsopen()
  */
@@ -547,12 +561,19 @@ static int init_sysapi(struct libmnt_context *cxt,
 	 *  is called later in hook_create_mount(). */
 	} else {
 		const char *type = mnt_fs_get_fstype(cxt->fs);
+		int rc = 0;
+
+		/* fsopen() to create a superblock */
+		if (cxt->helper == NULL && type && !strchr(type, ','))
+			rc = open_fs_configuration_context(cxt, api, type);
 
-		if (mnt_context_is_fake(cxt))
-			goto fake;
-		if (cxt->helper == NULL
-		    && type && !strchr(type, ',')
-		    && open_fs_configuration_context(cxt, api, type) < 0)
+		/* dummy fsopen() to test if API is available */
+		else if (!fsopen_is_supported()) {
+			errno = ENOSYS;
+			rc = -errno;
+			set_syscall_status(cxt, "fsopen", rc == 0);
+		}
+		if (rc < 0)
 			goto fail;
 	}