On Mon, Dec 27, 2010 at 7:18 PM, Gaurav Mahajan <gauravmahajan2007@xxxxxxxxx> wrote: > Hello all, > > Thanks for the information!!! > > > > On Mon, Dec 27, 2010 at 2:37 PM, Prasad Joshi <prasadjoshi124@xxxxxxxxx> wrote: >> On Mon, Dec 27, 2010 at 6:01 AM, Gaurav Mahajan >> <gauravmahajan2007@xxxxxxxxx> wrote: >>> Hi all, >>> >>> I have a doubt regarding the handling of bios. >>> >>> Suppose I receive a bio at some layer, and I want to split it into >>> multiple bios. There are layers below the one I am working on and the >>> final I/O operations will be handled by those layers. So, basically , >>> after some processing, I want to hand over the bio to the lower layer. >>> Now, if I have split the original bio into multiple bios and submitted >>> all the newly formed bios, I shall receive each such bio in the >>> bio->bio_end_io function. >>> >>> Here is it necessary to merge these bios so that the original bio can >>> be formed or is it ok to just split the original bio, receive the >>> requested data in multiple bios and leave it at that ? >>> >> >> IMHO, you still need to call bio->bio_end_io on the original BIO >> structure. So instead of splitting the original BIO. I think, You >> might want to keep the original BIO as it is. The smaller BIOs need to >> point back to original BIO and once all of the smaller BIOs have been >> serviced. You might want to call bio_end_io() on the original BIO. >> > > I think the method of pointing back to original bio, you wrote here is > about managing bi_idx fields of the split bios and keeping bio_vec > array same for all. Can you please elaborate on this, if I'm wrong? > > Also I wanted to split one bvec into two bvecs. So I tried to split it > using bvec's length and offset fields, but I am facing problem in > merging these split bvecs in one. Or there is some other way I can do > this? > > I am doubtful whether the pages are allocated for a bio when "read" is > requested or when the actual data is read from disk (at the layer of > I/O scheduler or device driver)? > I am not sure about this I did this some time back. As far as I can remember, I think I created multiple BIOs and used bi_private field to keep track of the parent BIOs and the number child BIOs. This new BIOs had their own end_io function. In the child_bio->end_io(), I would decrement the count of number of child BIOs. If the number is zero, call the end_io function of the parent BIO. Hope this helps. Speaking about the ordering of the BIOs, in my opinion, BIOs can be reodere by IO schedular. > >> Have a look if you can use bi_private field. >> >>> Looking forward to some help..... >>> >>> Regards, >>> Gaurav >>> >>> _______________________________________________ >>> Kernelnewbies mailing list >>> Kernelnewbies@xxxxxxxxxxxxxxxxx >>> http://lists.kernelnewbies.org/mailman/listinfo/kernelnewbies >>> >> > > Thanks, > Gaurav. > _______________________________________________ Kernelnewbies mailing list Kernelnewbies@xxxxxxxxxxxxxxxxx http://lists.kernelnewbies.org/mailman/listinfo/kernelnewbies
