[PATCH] kern/fs: honour file->read_hook in grub_fs_blocklist_read()

[Rasmus Villemoes]

Unlike files accessed via a normal file system, the file->read_hook is
not honoured when using blocklist notation.

This means that when trying to use a dedicated, 1KiB, raw partition
for the environment block and hence does something like

  save_env --file=(hd0,gpt9)0+2 X Y Z

this fails with "sparse file not allowed", which is rather unexpected,
as I've explicitly said exactly which blocks should be used. Adding a
little debugging reveals that grub_file_size (file) is 1024 as
expected, but total_length is 0, simply because the callback was never
invoked, so blocklists is an empty list.

Fix that by honouring the ->read_hook set by the caller, also when a
"file" is specified with blocklist notation.

Signed-off-by: Rasmus Villemoes <rasmus.villemoes@prevas.dk>
---
I've tried to keep the patch at a minimum, but since the
disk->read_hook needs to be cleared on all return paths, it seemed a
little easier to drop the 'return -1' and instead set ret and break.

For readability, it seemed best to introduce the disk local variable to
hold file->device->disk, and then there's no point in not also using
that in the grub_disk_read() call.

 grub-core/kern/fs.c | 11 +++++++++--
 1 file changed, 9 insertions(+), 2 deletions(-)

diff --git a/grub-core/kern/fs.c b/grub-core/kern/fs.c
index 7ad0aaf4e..79f1a797c 100644
--- a/grub-core/kern/fs.c
+++ b/grub-core/kern/fs.c
@@ -215,12 +215,15 @@ grub_fs_blocklist_read (grub_file_t file, char *buf, 
grub_size_t len)
   grub_disk_addr_t sector;
   grub_off_t offset;
   grub_ssize_t ret = 0;
+  grub_disk_t disk = file->device->disk;
 
   if (len > file->size - file->offset)
     len = file->size - file->offset;
 
   sector = (file->offset >> GRUB_DISK_SECTOR_BITS);
   offset = (file->offset & (GRUB_DISK_SECTOR_SIZE - 1));
+  disk->read_hook = file->read_hook;
+  disk->read_hook_data = file->read_hook_data;
   for (p = file->data; p->length && len > 0; p++)
     {
       if (sector < p->length)
@@ -232,9 +235,12 @@ grub_fs_blocklist_read (grub_file_t file, char *buf, 
grub_size_t len)
               >> GRUB_DISK_SECTOR_BITS) > p->length - sector)
            size = ((p->length - sector) << GRUB_DISK_SECTOR_BITS) - offset;
 
-         if (grub_disk_read (file->device->disk, p->offset + sector, offset,
+         if (grub_disk_read (disk, p->offset + sector, offset,
                              size, buf) != GRUB_ERR_NONE)
-           return -1;
+           {
+             ret = -1;
+             break;
+           }
 
          ret += size;
          len -= size;
@@ -244,6 +250,7 @@ grub_fs_blocklist_read (grub_file_t file, char *buf, 
grub_size_t len)
       else
        sector -= p->length;
     }
+  disk->read_hook = 0;
 
   return ret;
 }
-- 
2.46.0