Further information here:
http://www.kernel-labs.org/?q=blockdriver
http://www.kernel-labs.org/?q=blockiolayer
and kernel source drivers/block subdirectory, looking for all the
register_blkdev() caller, all these can be your potential block
devices examples. whether they used BIO or not it depends.
For example:
./brd.c:
if (register_blkdev(RAMDISK_MAJOR, "ramdisk"))
unregister_blkdev(RAMDISK_MAJOR, "ramdisk");
And inside brd.c look at how the API blk_queue_make_request() is used
for customization of special request structure, so bio is manipulated
in this brd.c.
But others like DAC960.c, virtio_blk.c etc does not touch the bio
internals, but deals at the request and request_queue level instead.
It leave the internals at the block/*.c implementation. For
example, for virtio_blk.c, it uses blk_rq_map_sg():
/*
* map a request to scatterlist, return number of sg entries setup. Caller
* must make sure sg can hold rq->nr_phys_segments entries
*/
int blk_rq_map_sg(struct request_queue *q, struct request *rq,
struct scatterlist *sglist)
{
struct bio_vec *bvec, *bvprv;
struct req_iterator iter;
struct scatterlist *sg;
for BIO mapping.
but then my generalization may be wrong?
On Wed, Sep 10, 2008 at 7:37 AM, Peter Teoh <[EMAIL PROTECTED]> wrote:
> On Wed, Sep 10, 2008 at 12:51 AM, Rohit Sharma <[EMAIL PROTECTED]> wrote:
>> I was going through block drivers,
>> i am not able to associate request queues and bio structures.
>> How are the requests processed using bio structures.
>> Can anyone provide me with block driver example or tutorial.
>>
>
> looking at block/scsi_ioctl.c:sg_io() function - does line 207 and 241
> answer your question?
>
> 207 rq = blk_get_request(q, writing ? WRITE : READ, GFP_KERNEL);
> 208 if (!rq)
> 209 return -ENOMEM;
> 210
> 211 if (blk_fill_sghdr_rq(q, rq, hdr, file)) {
> 212 blk_put_request(rq);
> 213 return -EFAULT;
> 214 }
> 215
> 216 if (hdr->iovec_count) {
> 217 const int size = sizeof(struct sg_iovec) *
> hdr->iovec_count;
> 218 struct sg_iovec *iov;
> 219
> 220 iov = kmalloc(size, GFP_KERNEL);
> 221 if (!iov) {
> 222 ret = -ENOMEM;
> 223 goto out;
> 224 }
> 225
> 226 if (copy_from_user(iov, hdr->dxferp, size)) {
> 227 kfree(iov);
> 228 ret = -EFAULT;
> 229 goto out;
> 230 }
> 231
> 232 ret = blk_rq_map_user_iov(q, rq, iov, hdr->iovec_count,
> 233 hdr->dxfer_len);
> 234 kfree(iov);
> 235 } else if (hdr->dxfer_len)
> 236 ret = blk_rq_map_user(q, rq, hdr->dxferp, hdr->dxfer_len);
> 237
> 238 if (ret)
> 239 goto out;
> 240
> 241 bio = rq->bio;
> 242 memset(sense, 0, sizeof(sense));
> 243 rq->sense = sense;
> 244 rq->sense_len = 0;
> 245 rq->retries = 0;
> 246
> 247 start_time = jiffies;
> 248
> 249 /* ignore return value. All information is passed back to caller
> 250 * (if he doesn't check that is his problem).
> 251 * N.B. a non-zero SCSI status is _not_ necessarily an error.
> 252 */
> 253 blk_execute_rq(q, bd_disk, rq, 0);
> 254
> 255 hdr->duration = jiffies_to_msecs(jiffies - start_time);
> 256
> 257 return blk_complete_sghdr_rq(rq, hdr, bio);
>
>
>
> --
> Regards,
> Peter Teoh
>
--
Regards,
Peter Teoh
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