Re: [PATCH] efidisk: Breakup large reads into batches

[Vladimir 'phcoder' Serbinenko]

Why is setting max_agglomerate not enough to achieve the same effect?

On Fri, Feb 23, 2024 at 8:12 PM Mate Kukri <mate.kukri@canonical.com> wrote:
>
> From: David F <davidf@terabyteunlimited.com>
>
> Work around firmware bugs that cause large reads to fail from certain
> devices.
>
> Report-By: David F <davidf@terabyteunlimited.com>
> Signed-off-by: Mate Kukri <mate.kukri@canonical.com>
> ---
>  grub-core/disk/efi/efidisk.c | 43 +++++++++++++++++++++++++-----------
>  1 file changed, 30 insertions(+), 13 deletions(-)
>
> diff --git a/grub-core/disk/efi/efidisk.c b/grub-core/disk/efi/efidisk.c
> index 3b5ed5691..079b72ab7 100644
> --- a/grub-core/disk/efi/efidisk.c
> +++ b/grub-core/disk/efi/efidisk.c
> @@ -27,6 +27,9 @@
>  #include <grub/efi/efi.h>
>  #include <grub/efi/disk.h>
>
> +/* break up io to prevent problems under some UEFI envrionments */
> +#define EFIDISK_C_MAXIOSECS 0x100U
> +
>  struct grub_efidisk_data
>  {
>    grub_efi_handle_t handle;
> @@ -599,20 +602,34 @@ grub_efidisk_read (struct grub_disk *disk, 
> grub_disk_addr_t sector,
>                    grub_size_t size, char *buf)
>  {
>    grub_efi_status_t status;
> +  grub_size_t sector_count;
>
> -  grub_dprintf ("efidisk",
> -               "reading 0x%lx sectors at the sector 0x%llx from %s\n",
> -               (unsigned long) size, (unsigned long long) sector, 
> disk->name);
> -
> -  status = grub_efidisk_readwrite (disk, sector, size, buf, 0);
> -
> -  if (status == GRUB_EFI_NO_MEDIA)
> -    return grub_error (GRUB_ERR_OUT_OF_RANGE, N_("no media in `%s'"), 
> disk->name);
> -  else if (status != GRUB_EFI_SUCCESS)
> -    return grub_error (GRUB_ERR_READ_ERROR,
> -                      N_("failure reading sector 0x%llx from `%s'"),
> -                      (unsigned long long) sector,
> -                      disk->name);
> +  /* break up reads to EFIDISK_C_MAXIOSECS size chunks */
> +  do
> +    {
> +      /* determine number of sectors this cycle */
> +      sector_count = (size > EFIDISK_C_MAXIOSECS) ? EFIDISK_C_MAXIOSECS : 
> size;
> +
> +      /* output debug information */
> +      grub_dprintf ("efidisk",
> +                   "reading 0x%lx sectors at the sector 0x%llx from %s\n",
> +                   (unsigned long) sector_count, (unsigned long long) 
> sector, disk->name);
> +
> +      status = grub_efidisk_readwrite (disk, sector, sector_count, buf, 0);
> +
> +      if (status == GRUB_EFI_NO_MEDIA)
> +       return grub_error (GRUB_ERR_OUT_OF_RANGE, N_("no media in `%s'"), 
> disk->name);
> +      if (status != GRUB_EFI_SUCCESS)
> +       return grub_error (GRUB_ERR_READ_ERROR,
> +                          N_("failure reading 0x%lx sector(s) from sector 
> 0x%llx on `%s'"),
> +                          (unsigned long) sector_count, (unsigned long long) 
> sector, disk->name);
> +
> +      /* next cycle */
> +      buf += (grub_efi_uintn_t) sector_count << disk->log_sector_size;;
> +      sector += sector_count;
> +      size -= sector_count;
> +    }
> +  while (size);
>
>    return GRUB_ERR_NONE;
>  }
> --
> 2.39.2
>
>
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-- 
Regards
Vladimir 'phcoder' Serbinenko