Introduce ERRNO_IS_FS_WRITE_REFUSED(), and use it in binfmt_mounted() (#38117)

- This introduces ERRNO_IS_FS_WRITE_REFUSED(), and apply it where
usable.
- This makes unexpected errors in access_fd() called by binfmt_mounted()
propagated to the caller.
- Renames binfmt_mounted() to binfmt_mounted_and_writable(), as it also
checks the fs is writable.
- Voidifies one disable_binfmt() call in shutdown.c.

src/shared/binfmt-util.c

@@ -11,7 +11,7 @@
 #include "missing_magic.h"
 #include "stat-util.h"
 
-int binfmt_mounted(void) {
+int binfmt_mounted_and_writable(void) {
         _cleanup_close_ int fd = -EBADF;
         int r;
 
@@ -25,7 +25,13 @@ int binfmt_mounted(void) {
         if (r <= 0)
                 return r;
 
-        return access_fd(fd, W_OK) >= 0;
+        r = access_fd(fd, W_OK);
+        if (ERRNO_IS_NEG_FS_WRITE_REFUSED(r))
+                return false;
+        if (r < 0)
+                return r;
+
+        return true;
 }
 
 int disable_binfmt(void) {
@@ -37,7 +43,7 @@ int disable_binfmt(void) {
          * We are a bit careful here, since binfmt_misc might still be an autofs which we don't want to
          * trigger. */
 
-        r = binfmt_mounted();
+        r = binfmt_mounted_and_writable();
         if (r < 0)
                 return log_warning_errno(r, "Failed to determine whether binfmt_misc is mounted: %m");
         if (r == 0) {

src/shared/binfmt-util.h

@@ -1,5 +1,5 @@
 /* SPDX-License-Identifier: LGPL-2.1-or-later */
 #pragma once
 
-int binfmt_mounted(void);
+int binfmt_mounted_and_writable(void);
 int disable_binfmt(void);

src/shared/loop-util.c

@@ -660,7 +660,7 @@ int loop_device_make_by_path_at(
                 r = fd;
 
                 /* Retry read-only? */
-                if (open_flags >= 0 || !(ERRNO_IS_PRIVILEGE(r) || r == -EROFS))
+                if (open_flags >= 0 || !ERRNO_IS_NEG_FS_WRITE_REFUSED(r))
                         return r;
 
                 fd = xopenat(dir_fd, path, basic_flags|direct_flags|O_RDONLY);