libglnx porting: Use glnx_set_error_from_errno

⚠️ There is a notable spiked pit trap here around
`posix_fallocate()` and `errno`.  This has bit other projects,
see e.g.
https://github.com/systemd/systemd/commit/7bb87460e691d30c1a7fd23a1a8240776957e05f

Otherwise the port was straightforward.

src/libotutil/ot-fs-utils.c

@@ -45,7 +45,7 @@ ot_gopendirat (int             dfd,
   int ret = ot_opendirat (dfd, path, follow);
   if (ret == -1)
     {
-      gs_set_error_from_errno (error, errno);
+      glnx_set_error_from_errno (error);
       return FALSE;
     }
   *out_fd = ret;
@@ -71,7 +71,7 @@ ot_lgetxattrat (int            dfd,
   while (G_UNLIKELY (bytes_read < 0 && errno == EINTR));
   if (G_UNLIKELY (bytes_read < 0))
     {
-      gs_set_error_from_errno (error, errno);
+      glnx_set_error_from_errno (error);
       goto out;
     }
 
@@ -81,7 +81,7 @@ ot_lgetxattrat (int            dfd,
   while (G_UNLIKELY (real_size < 0 && errno == EINTR));
   if (G_UNLIKELY (real_size < 0))
     {
-      gs_set_error_from_errno (error, errno);
+      glnx_set_error_from_errno (error);
       g_free (buf);
       goto out;
     }
@@ -111,7 +111,7 @@ ot_lsetxattrat (int            dfd,
   while (G_UNLIKELY (res == -1 && errno == EINTR));
   if (G_UNLIKELY (res == -1))
     {
-      gs_set_error_from_errno (error, errno);
+      glnx_set_error_from_errno (error);
       return FALSE;
     }
 
@@ -134,7 +134,7 @@ ot_readlinkat_gfile_info (int             dfd,
   while (G_UNLIKELY (len == -1 && errno == EINTR));
   if (len == -1)
     {
-      gs_set_error_from_errno (error, errno);
+      glnx_set_error_from_errno (error);
       goto out;
     }
   targetbuf[len] = '\0';
@@ -180,7 +180,7 @@ ot_openat_read_stream (int             dfd,
   while (G_UNLIKELY (fd == -1 && errno == EINTR));
   if (fd == -1)
     {
-      gs_set_error_from_errno (error, errno);
+      glnx_set_error_from_errno (error);
       goto out;
     }
 

src/libotutil/ot-gio-utils.c

@@ -309,7 +309,9 @@ ot_file_replace_contents_at (int             dfd,
       int r = posix_fallocate (fd, 0, g_bytes_get_size (contents));
       if (r != 0)
         {
-          gs_set_error_from_errno (error, r);
+          /* posix_fallocate is a weird deviation from errno standards */
+          errno = r;
+          glnx_set_error_from_errno (error);
           goto out;
         }
     }
@@ -320,7 +322,7 @@ ot_file_replace_contents_at (int             dfd,
 
   if (datasync && fdatasync (fd) != 0)
     {
-      gs_set_error_from_errno (error, errno);
+      glnx_set_error_from_errno (error);
       goto out;
     }
 
@@ -329,7 +331,7 @@ ot_file_replace_contents_at (int             dfd,
 
   if (renameat (dfd, tmpname, dfd, path) == -1)
     {
-      gs_set_error_from_errno (error, errno);
+      glnx_set_error_from_errno (error);
       goto out;
     }
 
@@ -429,7 +431,7 @@ ot_util_fsync_directory (GFile         *dir,
 
   if (fsync (dfd) != 0)
     {
-      gs_set_error_from_errno (error, errno);
+      glnx_set_error_from_errno (error);
       goto out;
     }
 

src/libotutil/ot-variant-utils.c

@@ -204,7 +204,7 @@ ot_util_variant_map_fd (int                    fd,
 
   if (fstat (fd, &stbuf) != 0)
     {
-      gs_set_error_from_errno (error, errno);
+      glnx_set_error_from_errno (error);
       goto out;
     }
 
@@ -212,7 +212,7 @@ ot_util_variant_map_fd (int                    fd,
   map = mmap (NULL, len, PROT_READ, MAP_PRIVATE, fd, start);
   if (!map)
     {
-      gs_set_error_from_errno (error, errno);
+      glnx_set_error_from_errno (error);
       goto out;
     }