On Thu, Sep 13, 2018 at 03:20:34PM +0800, Michael Chang wrote:
> In grub-core/osdep/linux/hostdisk.c::grub_util_fd_open_device() there's
> comment
> about linux disk cache issue as below:
>
> /* Linux has a bug that the disk cache for a whole disk is not consistent
> with the one for a partition of the disk. */
> {
> ....
> }
>
> As the input argument of grub_util_fd_open_device() is using address in unit
> of
> sector size offset from the "disk", and in a bid to avoid Linux disk cache
> inconsistency problem described by comment above, grub translates the address
> again into the address offset from partition that has encompassed it, then use
> that partition device in place of disk device.
>
> The problem we encountered was that installing grub into multipath disk's
> partition didn't work reliably. It boiled down to the disk cache problem
> described above as strace result shown it was still using the whole disk
> device, not the partition device we would expect.
>
> This patch fixes the problem by adding the missing "/dev/dm-" name scheme
> handling in grub_hostdisk_linux_find_partition(). After applying the patch
> problem gets solved and we would like to have this fixing patch upstreamed as
> it looks good material to be.
>
> v1: Rework commit message.
Thanks! Right now it looks much better for me.
> Signed-off-by: Michael Chang <mch...@suse.com>
> ---
> grub-core/osdep/linux/hostdisk.c | 6 ++++++
> 1 file changed, 6 insertions(+)
>
> diff --git a/grub-core/osdep/linux/hostdisk.c
> b/grub-core/osdep/linux/hostdisk.c
> index 06179fca7..ed530bdc4 100644
> --- a/grub-core/osdep/linux/hostdisk.c
> +++ b/grub-core/osdep/linux/hostdisk.c
> @@ -263,6 +263,12 @@ grub_hostdisk_linux_find_partition (char *dev,
> grub_disk_addr_t sector)
> p = real_dev + len;
> format = "-part%d";
> }
> + else if (strncmp (real_dev, "/dev/dm-",
> + sizeof ("/dev/dm-") - 1) == 0)
> + {
> + p = real_dev + len - 1;
> + format = "%d";
> + }
What will happen if the device path is /dev/dm-10?
> else if (real_dev[len - 1] >= '0' && real_dev[len - 1] <= '9')
> {
> p = real_dev + len;
...and I am afraid that above line is buggy too...
What about the other cases?
Daniel
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