Hi Mike, Thank you for the super prompt reply. I actually downloaded that book a while but never read. I'm gonna start reading right away. Thanks a lot for telling me.
Two more questions about open-iscsi implementaion though.. 1. As you mentioned in a previous reply, open-iscsi only supports one page in one sg entry, is there any specific reason behind that? and would it be possible to enable " scsi_host_template::use_clustering"? 2. I looked at the way sendpage() is used in iscsi_tcp.c and it seems like we are sending one sg entry per sendpage() call. I was wondering would it possible to send more than one sg entries per at one time, say we copy a few pages to one buffer fist and then send out that buffer through sendpage()? Thank you very much. Jack On May 6, 3:08 pm, Mike Christie <micha...@cs.wisc.edu> wrote: > On 05/06/2010 03:53 PM, Jack Z wrote: > > > Hi Mike, > > > Thanks for your reply. > > > What I was doing was just trying to understand how the the data > > travels through normal fs or block layer, reaches iscsi and gets sent > > over the network, when there is a normal read()/write() request. So > > the function call trace I have found is not quite the normal path? > > Yeah, it is the passthrough one. But once it gets to the iscsi layer's > iscsi_queuecommand function it is all the same. > > > Actually I'm still new to the kernel and the storage subsystem... So > > could you maybe tell me what I should look at to learn more about the > > normal code path of a read/write request? Or maybe point me to some > > online materials/books I can gain some understanding from? > > Do you have the Linux Device Driver book? It is > free:http://lwn.net/Kernel/LDD3/. Chapter 16 starting with the section > Request Processing might be helpful. It might be a little dated, but the > bio to request processing and a lot of the request and request queue > processing is close. I think it can be used to help find a function in > the current kernel and from there it seems like you can figure out where > things are going. > > > > > Thanks a lot! > > > Jack > > > On May 6, 10:56 am, Mike Christie<micha...@cs.wisc.edu> wrote: > >> On 05/05/2010 10:26 PM, Jack Z wrote: > > >>> Hi Mike, > > >>> Thank you for your help again. Following the guidance in your reply, I > >>> traced the kernel code a bit more and eventually found out a possible > >>> path for open-iscsi to get 4K pages in the scatterlist. > > >>> Kernel version: 2.6.30 > >>> open-iscsi version: 2.0.871 > > >>> Trace 1: SCSI from a write request to data written into pages > > >>> --> function pointer > > >>> sg_fops.write --> sg_write() > > >> Just so you know, this is the passthrough path. You are using some tools > >> like sg_utils or doing SG IO right? > > >> What I described might be a little different than this path. I was > >> describing the normal FS/Block layer code path (like when you do a > >> read()/write() to /dev/sda or to some file on a FS on /dev/sda). > > >> -- > >> You received this message because you are subscribed to the Google Groups > >> "open-iscsi" group. > >> To post to this group, send email to open-is...@googlegroups.com. > >> To unsubscribe from this group, send email to > >> open-iscsi+unsubscr...@googlegroups.com. > >> For more options, visit this group > >> athttp://groups.google.com/group/open-iscsi?hl=en. > > -- > You received this message because you are subscribed to the Google Groups > "open-iscsi" group. > To post to this group, send email to open-is...@googlegroups.com. > To unsubscribe from this group, send email to > open-iscsi+unsubscr...@googlegroups.com. > For more options, visit this group > athttp://groups.google.com/group/open-iscsi?hl=en. -- You received this message because you are subscribed to the Google Groups "open-iscsi" group. To post to this group, send email to open-is...@googlegroups.com. To unsubscribe from this group, send email to open-iscsi+unsubscr...@googlegroups.com. For more options, visit this group at http://groups.google.com/group/open-iscsi?hl=en.
