[GEDI] [PATCH v3 01/17] block/throttle-groups: throttle_group_co_io_limits_intercept(): 64bit bytes

Alberto Garcia berto at igalia.com
Mon May 11 15:28:12 UTC 2020

On Thu 30 Apr 2020 01:10:17 PM CEST, Vladimir Sementsov-Ogievskiy wrote:
> The function is called from 64bit io handlers, and bytes is just passed
> to throttle_account() which is 64bit too (unsigned though). So, let's
> convert intermediate argument to 64bit too.
> This patch is a first in the 64-bit-blocklayer series, so we are
> generally moving to int64_t for both offset and bytes parameters on all
> io paths. Main motivation is realization of 64-bit write_zeroes
> operation for fast zeroing large disk chunks, up to the whole disk.
> We chose signed type, to be consistent with off_t (which is signed) and
> with possibility for signed return type (where negative value means
> error).
> Patch-correctness audit by Eric Blake:
>   Caller has 32-bit, this patch now causes widening which is safe:
>   block/block-backend.c: blk_do_preadv() passes 'unsigned int'
>   block/block-backend.c: blk_do_pwritev_part() passes 'unsigned int'
>   block/throttle.c: throttle_co_pwrite_zeroes() passes 'int'
>   block/throttle.c: throttle_co_pdiscard() passes 'int'
>   Caller has 64-bit, this patch fixes potential bug where pre-patch
>   could narrow, except it's easy enough to trace that callers are still
>   capped at 2G actions:
>   block/throttle.c: throttle_co_preadv() passes 'uint64_t'
>   block/throttle.c: throttle_co_pwritev() passes 'uint64_t'
>   Implementation in question: block/throttle-groups.c
>   throttle_group_co_io_limits_intercept() takes 'unsigned int bytes'
>   and uses it: argument to util/throttle.c throttle_account(uint64_t)
>   All safe: it patches a latent bug, and does not introduce any 64-bit
>   gotchas once throttle_co_p{read,write}v are relaxed, and assuming
>   throttle_account() is not buggy.
> Series: 64bit-block-status
> Signed-off-by: Vladimir Sementsov-Ogievskiy <vsementsov at virtuozzo.com>
> Reviewed-by: Eric Blake <eblake at redhat.com>

Reviewed-by: Alberto Garcia <berto at igalia.com>


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