u-boot: add 'bootdir' to the generated uEnv.txt

When doing a full copy of:

$deployment/usr/lib/ostree-boot -> /boot/ostree/$os-$bootcsum/

U-Boot bootscript can use the 'bootdir' to find, for example,
the Device Tree (dtb) file, as in:

load ${dtype} ${disk}:${bootpart} ${a_fdt} ${bootdir}${dtbname}

Or u-boot external bootscript:

load ${dtype} ${disk}:${bootpart} ${a_scr} ${bootdir}${scriptname}

It could also be possible to point 'bootdir' directly to the
$deployment/usr/lib/ostree-boot, but this would add unnecessary
restrictions on what file system can be used for rootfs as u-boot,
for example, can not read from BTRFS. So having
bootdir=/boot/ostree/$os-$bootcsum/ is a better approach here, as
/boot can be on a separate partition with its own file system type.

Signed-off-by: Gatis Paeglis <[email protected]>
Signed-off-by: Hongxu Jia <[email protected]>
Signed-off-by: Chen Qi <[email protected]>

src/libostree/ostree-bootloader-uboot.c

@@ -114,6 +114,7 @@ create_config_from_boot_loader_entries (OstreeBootloaderUboot *self, int bootver
   for (int i = 0; i < boot_loader_configs->len; i++)
     {
       g_autofree char *index_suffix = NULL;
+      g_autofree char *bootdir = NULL;
       if (i == 0)
         index_suffix = g_strdup ("");
       else
@@ -129,6 +130,9 @@ create_config_from_boot_loader_entries (OstreeBootloaderUboot *self, int bootver
         }
       g_ptr_array_add (new_lines, g_strdup_printf ("kernel_image%s=/boot%s", index_suffix, val));
 
+      bootdir = strndup (val, strrchr(val, '/') - val);
+      g_ptr_array_add (new_lines, g_strdup_printf ("bootdir%s=%s/", index_suffix, bootdir));
+
       val = ostree_bootconfig_parser_get (config, "initrd");
       if (val)
         g_ptr_array_add (new_lines, g_strdup_printf ("ramdisk_image%s=/boot%s", index_suffix, val));