Re: [PATCH 4/4] block: Integrity profile init function to trigger module loads

[Ard Biesheuvel]

Hi Martin,

On 26 August 2018 at 03:40, Martin K. Petersen
<martin.petersen@xxxxxxxxxx> wrote:
> The T10 CRC library function is built into the kernel and therefore
> registered early. The hardware-accelerated CRC helpers are typically
> loaded as modules and only become available later in the boot
> sequence. A separate patch modifies the T10 CRC library to subscribe
> to notifications from crypto and permits switching from the
> table-based algorithm to a hardware accelerated ditto once the
> relevant module is loaded.
>
> However, since the dependency for "crc10dif" is already satisfied,
> nothing is going to cause the hardware-accelerated kernel modules to
> get loaded.

This is not true. All accelerated implementations based on SIMD
polynomial multiplication are tried to the respective CPU features
bits. This applies to x86, power, ARM and arm64.

E.g., for x86 you have

alias:          cpu:type:x86,ven*fam*mod*:feature:*0081*

which will be matched by udev if /sys/devices/system/cpu/modalias
contains feature 0081, and so the modules will be loaded automatically
at boot.



> Introduce an init_fn in the integrity profile that can be
> called to trigger a load of modules providing the T10 CRC calculation
> capability. This function will ony get called when a new integrity
> profile is registered during device discovery.
>
> Signed-off-by: Martin K. Petersen <martin.petersen@xxxxxxxxxx>
> ---
>  block/blk-integrity.c  |  5 +++++
>  block/t10-pi.c         | 10 ++++++++++
>  include/linux/blkdev.h |  2 ++
>  3 files changed, 17 insertions(+)
>
> diff --git a/block/blk-integrity.c b/block/blk-integrity.c
> index 6121611e1316..5cacae9a2dc2 100644
> --- a/block/blk-integrity.c
> +++ b/block/blk-integrity.c
> @@ -27,6 +27,7 @@
>  #include <linux/scatterlist.h>
>  #include <linux/export.h>
>  #include <linux/slab.h>
> +#include <linux/module.h>
>
>  #include "blk.h"
>
> @@ -391,6 +392,7 @@ static blk_status_t blk_integrity_nop_fn(struct blk_integrity_iter *iter)
>
>  static const struct blk_integrity_profile nop_profile = {
>         .name = "nop",
> +       .init_fn = NULL,
>         .generate_fn = blk_integrity_nop_fn,
>         .verify_fn = blk_integrity_nop_fn,
>  };
> @@ -418,6 +420,9 @@ void blk_integrity_register(struct gendisk *disk, struct blk_integrity *template
>         bi->tuple_size = template->tuple_size;
>         bi->tag_size = template->tag_size;
>
> +       if (bi->profile->init_fn)
> +               bi->profile->init_fn();
> +
>         disk->queue->backing_dev_info->capabilities |= BDI_CAP_STABLE_WRITES;
>  }
>  EXPORT_SYMBOL(blk_integrity_register);
> diff --git a/block/t10-pi.c b/block/t10-pi.c
> index a98db384048f..b83278f9163a 100644
> --- a/block/t10-pi.c
> +++ b/block/t10-pi.c
> @@ -24,6 +24,7 @@
>  #include <linux/t10-pi.h>
>  #include <linux/blkdev.h>
>  #include <linux/crc-t10dif.h>
> +#include <linux/module.h>
>  #include <net/checksum.h>
>
>  typedef __be16 (csum_fn) (void *, unsigned int);
> @@ -157,8 +158,14 @@ static blk_status_t t10_pi_type3_verify_ip(struct blk_integrity_iter *iter)
>         return t10_pi_verify(iter, t10_pi_ip_fn, 3);
>  }
>
> +static void t10_pi_crc_init(void)
> +{
> +       request_module_nowait(CRC_T10DIF_STRING);
> +}
> +
>  const struct blk_integrity_profile t10_pi_type1_crc = {
>         .name                   = "T10-DIF-TYPE1-CRC",
> +       .init_fn                = t10_pi_crc_init,
>         .generate_fn            = t10_pi_type1_generate_crc,
>         .verify_fn              = t10_pi_type1_verify_crc,
>  };
> @@ -166,6 +173,7 @@ EXPORT_SYMBOL(t10_pi_type1_crc);
>
>  const struct blk_integrity_profile t10_pi_type1_ip = {
>         .name                   = "T10-DIF-TYPE1-IP",
> +       .init_fn                = NULL,
>         .generate_fn            = t10_pi_type1_generate_ip,
>         .verify_fn              = t10_pi_type1_verify_ip,
>  };
> @@ -173,6 +181,7 @@ EXPORT_SYMBOL(t10_pi_type1_ip);
>
>  const struct blk_integrity_profile t10_pi_type3_crc = {
>         .name                   = "T10-DIF-TYPE3-CRC",
> +       .init_fn                = t10_pi_crc_init,
>         .generate_fn            = t10_pi_type3_generate_crc,
>         .verify_fn              = t10_pi_type3_verify_crc,
>  };
> @@ -180,6 +189,7 @@ EXPORT_SYMBOL(t10_pi_type3_crc);
>
>  const struct blk_integrity_profile t10_pi_type3_ip = {
>         .name                   = "T10-DIF-TYPE3-IP",
> +       .init_fn                = NULL,
>         .generate_fn            = t10_pi_type3_generate_ip,
>         .verify_fn              = t10_pi_type3_verify_ip,
>  };
> diff --git a/include/linux/blkdev.h b/include/linux/blkdev.h
> index 79226ca8f80f..a43c02e4f43d 100644
> --- a/include/linux/blkdev.h
> +++ b/include/linux/blkdev.h
> @@ -1806,10 +1806,12 @@ struct blk_integrity_iter {
>  };
>
>  typedef blk_status_t (integrity_processing_fn) (struct blk_integrity_iter *);
> +typedef void (integrity_init_fn) (void);
>
>  struct blk_integrity_profile {
>         integrity_processing_fn         *generate_fn;
>         integrity_processing_fn         *verify_fn;
> +       integrity_init_fn               *init_fn;
>         const char                      *name;
>  };
>
> --
> 2.17.1
>