BIO_ALLOC_BIOSET(9)                       The Linux VFS                       BIO_ALLOC_BIOSET(9)



NAME
       bio_alloc_bioset - allocate a bio for I/O

SYNOPSIS
       struct bio * bio_alloc_bioset(gfp_t gfp_mask, int nr_iovecs, struct bio_set * bs);

ARGUMENTS
       gfp_mask
           the GFP_ mask given to the slab allocator

       nr_iovecs
           number of iovecs to pre-allocate

       bs
           the bio_set to allocate from.

DESCRIPTION
       If bs is NULL, uses kmalloc to allocate the bio; else the allocation is backed by the bs's
       mempool.

       When bs is not NULL, if __GFP_DIRECT_RECLAIM is set then bio_alloc will always be able to
       allocate a bio. This is due to the mempool guarantees. To make this work, callers must
       never allocate more than 1 bio at a time from this pool. Callers that need to allocate
       more than 1 bio must always submit the previously allocated bio for IO before attempting
       to allocate a new one. Failure to do so can cause deadlocks under memory pressure.

       Note that when running under generic_make_request (i.e. any block driver), bios are not
       submitted until after you return - see the code in generic_make_request that converts
       recursion into iteration, to prevent stack overflows.

       This would normally mean allocating multiple bios under generic_make_request would be
       susceptible to deadlocks, but we have deadlock avoidance code that resubmits any blocked
       bios from a rescuer thread.

       However, we do not guarantee forward progress for allocations from other mempools. Doing
       multiple allocations from the same mempool under generic_make_request should be avoided -
       instead, use bio_set's front_pad for per bio allocations.

RETURN
       Pointer to new bio on success, NULL on failure.

COPYRIGHT
Kernel Hackers Manual 4.8.                 January 2017                       BIO_ALLOC_BIOSET(9)