sd-journal: make prot_from_flags() static and rename

The function had just one caller and a name that didn't explain much.
Let's make it static and rename for clarity.

While at it, the only caller was not doing error handling correctly
— the function would potentially return a negative error value which
wasn't handled. In practice this couldn't happen, but let's remove
this ambiguity.

src/basic/util.c

@@ -23,24 +23,6 @@ int saved_argc = 0;
 char **saved_argv = NULL;
 static int saved_in_initrd = -1;
 
-int prot_from_flags(int flags) {
-
-        switch (flags & O_ACCMODE) {
-
-        case O_RDONLY:
-                return PROT_READ;
-
-        case O_WRONLY:
-                return PROT_WRITE;
-
-        case O_RDWR:
-                return PROT_READ|PROT_WRITE;
-
-        default:
-                return -EINVAL;
-        }
-}
-
 bool in_initrd(void) {
         int r;
         const char *e;

src/basic/util.h

@@ -19,8 +19,6 @@ static inline void save_argc_argv(int argc, char **argv) {
         saved_argv = argv;
 }
 
-int prot_from_flags(int flags) _const_;
-
 bool in_initrd(void);
 void in_initrd_force(bool value);
 

src/libsystemd/sd-journal/journal-file.c

@@ -92,6 +92,19 @@
 #  pragma GCC diagnostic ignored "-Waddress-of-packed-member"
 #endif
 
+static int mmap_prot_from_open_flags(int flags) {
+        switch (flags & O_ACCMODE) {
+        case O_RDONLY:
+                return PROT_READ;
+        case O_WRONLY:
+                return PROT_WRITE;
+        case O_RDWR:
+                return PROT_READ|PROT_WRITE;
+        default:
+                assert_not_reached();
+        }
+}
+
 int journal_file_tail_end_by_pread(JournalFile *f, uint64_t *ret_offset) {
         uint64_t p;
         int r;
@@ -3767,7 +3780,7 @@ int journal_file_open(
                 newly_created = f->last_stat.st_size == 0 && journal_file_writable(f);
         }
 
-        f->cache_fd = mmap_cache_add_fd(mmap_cache, f->fd, prot_from_flags(open_flags));
+        f->cache_fd = mmap_cache_add_fd(mmap_cache, f->fd, mmap_prot_from_open_flags(open_flags));
         if (!f->cache_fd) {
                 r = -ENOMEM;
                 goto fail;