[PATCH v2 3/9] util/grub-editenv: add fs_envblk write helper

[Michael Chang via Grub-devel <grub-devel@gnu.org>]

This patch adds the function fs_envblk_write to update the reserved
environment block on disk. The helper takes an in memory envblk buffer
and writes it back to the device at the location defined by the
fs_envblk specification. It performs size checks and uses file sync to
ensure that the updated data is flushed.

The helper is also added into the fs_envblk ops table, together with the
open helper from the previous patch. With this change the basic input
and output path for an external environment block is complete. The
choice of which variables should be written externally will be handled
by later patches.

Signed-off-by: Michael Chang <mchang@suse.com>
---
 util/grub-editenv.c | 38 +++++++++++++++++++++++++++++++++++++-
 1 file changed, 37 insertions(+), 1 deletion(-)

diff --git a/util/grub-editenv.c b/util/grub-editenv.c
index 4e5dffa86..26a81d2d0 100644
--- a/util/grub-editenv.c
+++ b/util/grub-editenv.c
@@ -131,9 +131,11 @@ struct fs_envblk_spec {
 typedef struct fs_envblk_spec *fs_envblk_spec_t;
 
 static grub_envblk_t fs_envblk_open (grub_envblk_t envblk);
+static void fs_envblk_write (grub_envblk_t envblk);
 
 struct fs_envblk_ops {
   grub_envblk_t (*open) (grub_envblk_t);
+  void (*write) (grub_envblk_t);
 };
 
 struct fs_envblk {
@@ -144,7 +146,8 @@ struct fs_envblk {
 typedef struct fs_envblk *fs_envblk_t;
 
 static struct fs_envblk_ops fs_envblk_ops = {
-  .open = fs_envblk_open
+  .open = fs_envblk_open,
+  .write = fs_envblk_write
 };
 
 static struct fs_envblk_spec fs_envblk_spec[] = {
@@ -358,6 +361,39 @@ write_envblk (const char *name, grub_envblk_t envblk)
   fclose (fp);
 }
 
+static void
+fs_envblk_write (grub_envblk_t envblk)
+{
+  FILE *fp;
+  const char *device;
+  off_t offset;
+  size_t size;
+
+  if (envblk == NULL)
+    return;
+
+  device = fs_envblk->dev;
+  offset = fs_envblk->spec->offset;
+  size = fs_envblk->spec->size;
+
+  if (grub_envblk_size (envblk) > size)
+    grub_util_error ("%s", _("environment block too small"));
+
+  fp = grub_util_fopen (device, "r+b");
+
+  if (! fp)
+    grub_util_error (_("cannot open `%s': %s"), device, strerror (errno));
+
+  if (fseek (fp, offset, SEEK_SET) < 0)
+    grub_util_error (_("cannot seek `%s': %s"), device, strerror (errno));
+
+  if (fwrite (grub_envblk_buffer (envblk), 1, grub_envblk_size (envblk), fp) != grub_envblk_size (envblk))
+    grub_util_error (_("cannot write to `%s': %s"), device, strerror (errno));
+
+  grub_util_file_sync (fp);
+  fclose (fp);
+}
+
 static void
 set_variables (const char *name, int argc, char *argv[])
 {
-- 
2.51.0


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