1BLK_MAKE_REQUEST(9)              Block Devices             BLK_MAKE_REQUEST(9)
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NAME

6       blk_make_request - given a bio, allocate a corresponding struct
7       request.
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SYNOPSIS

10       struct request * blk_make_request(struct request_queue * q,
11                                         struct bio * bio, gfp_t gfp_mask);
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ARGUMENTS

14       q
15           target request queue
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17       bio
18           The bio describing the memory mappings that will be submitted for
19           IO. It may be a chained-bio properly constructed by block/bio
20           layer.
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22       gfp_mask
23           gfp flags to be used for memory allocation
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DESCRIPTION

26       blk_make_request is the parallel of generic_make_request for BLOCK_PC
27       type commands. Where the struct request needs to be farther initialized
28       by the caller. It is passed a struct bio, which describes the memory
29       info of the I/O transfer.
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31       The caller of blk_make_request must make sure that bi_io_vec are set to
32       describe the memory buffers. That bio_data_dir will return the needed
33       direction of the request. (And all bio's in the passed bio-chain are
34       properly set accordingly)
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36       If called under none-sleepable conditions, mapped bio buffers must not
37       need bouncing, by calling the appropriate masked or flagged allocator,
38       suitable for the target device. Otherwise the call to blk_queue_bounce
39       will BUG.
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WARNING

42       When allocating/cloning a bio-chain, careful consideration should be
43       given to how you allocate bios. In particular, you cannot use
44       __GFP_WAIT for anything but the first bio in the chain. Otherwise you
45       risk waiting for IO completion of a bio that hasn't been submitted yet,
46       thus resulting in a deadlock. Alternatively bios should be allocated
47       using bio_kmalloc instead of bio_alloc, as that avoids the mempool
48       deadlock. If possible a big IO should be split into smaller parts when
49       allocation fails. Partial allocation should not be an error, or you
50       risk a live-lock.
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53Kernel Hackers Manual 2.6.       November 2011             BLK_MAKE_REQUEST(9)
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