util/grub-editenv: Wire set_variables() to optional fs_envblk

This patch changes set_variables() so that it can use an external
environment block when one is present. The variable next_entry is
written into the external block, env_block is treated as read only, and
all other variables are written into the normal file based envblk.

A cleanup step is added to handle cases where GRUB at runtime writes
variables into the external block because file based updates are not
safe on a copy on write filesystem such as Btrfs. For example, the
savedefault command can update saved_entry, and on Btrfs GRUB will place
that update in the external block instead of the file envblk. If an
older copy remains in the external block, it would override the newer
value from the file envblk when GRUB first loads the file and then
applies the external block on top of it. To avoid this, whenever
a variable is updated in the file envblk, any same named key in
the external block is deleted.

Signed-off-by: Michael Chang <mchang@suse.com>
Reviewed-by: Neal Gompa <ngompa13@gmail.com>
Reviewed-by: Avnish Chouhan <avnish@linux.ibm.com>
Reviewed-by: Daniel Kiper <daniel.kiper@oracle.com>

diff --git a/util/grub-editenv.c b/util/grub-editenv.c
index c1a8a5117c3bc34eb032c7b31c7ba0df4c4cbaf4..7d4981d673c4f24c3dd362f4f7c1871ddea467e7 100644 (file)
--- a/util/grub-editenv.c
+++ b/util/grub-editenv.c
@@ -414,12 +414,35 @@ fs_envblk_write (grub_envblk_t envblk)
   fclose (fp);
 }
 
+struct var_lookup_ctx {
+  const char *varname;
+  bool found;
+};
+typedef struct var_lookup_ctx var_lookup_ctx_t;
+
+static int
+var_lookup_iter (const char *varname, const char *value __attribute__ ((unused)), void *hook_data)
+{
+  var_lookup_ctx_t *ctx = (var_lookup_ctx_t *) hook_data;
+
+  if (grub_strcmp (ctx->varname, varname) == 0)
+    {
+      ctx->found = true;
+      return 1;
+    }
+  return 0;
+}
+
 static void
 set_variables (const char *name, int argc, char *argv[])
 {
   grub_envblk_t envblk;
+  grub_envblk_t envblk_on_block = NULL;
 
   envblk = open_envblk_file (name);
+  if (fs_envblk != NULL)
+    envblk_on_block = fs_envblk->ops->open (envblk);
+
   while (argc)
     {
       char *p;
@@ -430,15 +453,46 @@ set_variables (const char *name, int argc, char *argv[])
 
       *(p++) = 0;
 
-      if (! grub_envblk_set (envblk, argv[0], p))
-        grub_util_error ("%s", _("environment block too small"));
+      if ((strcmp (argv[0], "next_entry") == 0) && envblk_on_block != NULL)
+       {
+         if (grub_envblk_set (envblk_on_block, argv[0], p) == 0)
+           grub_util_error ("%s", _("environment block too small"));
+         goto next;
+       }
+
+      if (strcmp (argv[0], "env_block") == 0)
+       {
+         grub_util_warn (_("can't set env_block as it's read-only"));
+         goto next;
+       }
+
+      if (grub_envblk_set (envblk, argv[0], p) == 0)
+       grub_util_error ("%s", _("environment block too small"));
 
+      if (envblk_on_block != NULL)
+       {
+         var_lookup_ctx_t ctx = {
+           .varname = argv[0],
+           .found = false
+         };
+
+         grub_envblk_iterate (envblk_on_block, &ctx, var_lookup_iter);
+         if (ctx.found == true)
+           grub_envblk_delete (envblk_on_block, argv[0]);
+       }
+ next:
       argc--;
       argv++;
     }
 
   write_envblk (name, envblk);
   grub_envblk_close (envblk);
+
+  if (envblk_on_block != NULL)
+    {
+      fs_envblk->ops->write (envblk_on_block);
+      grub_envblk_close (envblk_on_block);
+    }
 }
 
 static void