Re: Query about Bio submission / Direct IO

2007-10-22 Thread Shreyansh 
Hi list and Boaz,

On 10/22/07, Boaz Harrosh <[EMAIL PROTECTED]> wrote:
> On Fri, Oct 19 2007 at 8:17 +0200, Shreyansh Jain <[EMAIL PROTECTED]> wrote:
> > Hi List,
> >
---8<-
> > Any idea why it doesn't work (though I am expecting that this doc is 2.6
> > starting era and things might have changed a lot now).
> >
> > Any help would be highly appreciated. Apologies if my channel of approach is
> > wrong and if this post is huge (couldn't keep it shorter than this).
> >
> > Shreyansh
> >
> >
> > [PS: Is this situation something to do with request flags REQ_PC /
> > REQ_BLOCK_PC?? While searching code, I found these somewhere connected to
> > direct IO (bio_add_pc_page) and could find more about them]
> >
--8<--
> > -
>
> There was a related fix to a similar problem by Mike Christie, in resent
> Kernels, If there is no chance for you working on newer kernels, than you
> will have to back port it.
>
> it is:
> commit bd441deaf341c524b28fd72831ebf6fef88f1c41
> Author: Mike Christie <[EMAIL PROTECTED]>
> Date:   Tue Mar 13 12:52:29 2007 -0500

Thanks a lot for pointing that out to me. I will have a look at that.

>
> [SCSI] fix write buffer length in scsi_req_map_sg()
>
>
> look it up the git trees on kernel.org

Certainly I will do that :) ... Thanks

>
> Boaz
>

Shreyansh
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Re: Query about Bio submission / Direct IO

2007-10-22 Thread Boaz Harrosh 
On Fri, Oct 19 2007 at 8:17 +0200, Shreyansh Jain <[EMAIL PROTECTED]> wrote:
> Hi List,
> 
> I have tried this on kernelnewbies
>  but it 
> seems 
> I am not good at explaining well. trying here again.
> 
> Question:
> Is there a limitation (some kind of caveat) when direct IO pages are added to 
> a bio (multiple pages per bio) and if the total length or offset of some of 
> the vectors is not aligned (PAGE_SIZE or sector size)?
> 
> My scenario:
> 1. I have a filesystem in which I create bio for submission to a SCSI disk 
>connected in a SAN via a FC switch. 
> 2. This is a direct IO request where in multiple pages are being added in a 
> bio
>(bio_map_user). Also, as the user buffer I get is unaligned, I am changing
> bio's first vector offset (as well as len, bi_size accordingly).
> 
> What I observe is:
> 
> 1. IO is performed perfectly (as expected) in case there are no SCSI failure.
>end_bio gets called as expected and the user app is happy.
> 2. In case I  disconnect the SCSI device from switch, my end_bio function 
>keeps on getting sub-completion bio (bi_size > 0 and uptodate cleared,
>error set to -5).
> 3. For capturing and ignoring sub-completion returns from block layer, 
>using other kernel end_bio implementation as example I had a code like
> 
> if(bio->bi_size > 0)
>return 1;
> 
>as the starting lines of the end_bio routine. Thus, my user space goes off 
>to disk sleep and kernel log keeps on spweing messages like 
> 
> ...
> Oct 17 21:56:07 mgs02 kernel: end_request: I/O error, dev sdl, sector 33639
> Oct 17 21:56:07 mgs02 kernel: sd 2:0:0:8: SCSI error: return code = 0x1
> Oct 17 21:56:07 mgs02 kernel: end_request: I/O error, dev sdl, sector 33639
> Oct 17 21:56:07 mgs02 kernel: sd 2:0:0:8: SCSI error: return code = 0x1
> Oct 17 21:56:07 mgs02 kernel: end_request: I/O error, dev sdl, sector 33639
> ...
> 
> till i connect the switch back - even if that is one hour after disconnecting 
> it.
> 
> Best part - it works amazingly well in case I keep the offset of the first 
> page
> aligned (somehow, at expense of corrupted data copy) - failure of SCSI disk
> (end_bio returns, bi_size=0, my code captures error) or no failure.
> 
> I have tried this on 2.6.5 and 2.6.16.27 (I agree they are old, but that is 
> what I have to work  on :( ). It is a qlogic SCSI HBA. I have created the bio
>  just like other kernel subsystems do.
> 
> Only thing I am not sure is whether there is something special that needs to 
> be done in case of direct IO which I am missing.
> 
> biodoc.txt states that:
> "Note: Right now the only user of bios with more than one page is ll_rw_kio,
>  which in turn means that only raw I/O uses it (direct i/o may not work right
>  now)."
> 
> Any idea why it doesn't work (though I am expecting that this doc is 2.6
> starting era and things might have changed a lot now).
> 
> Any help would be highly appreciated. Apologies if my channel of approach is
> wrong and if this post is huge (couldn't keep it shorter than this).
> 
> Shreyansh
> 
> 
> [PS: Is this situation something to do with request flags REQ_PC /
> REQ_BLOCK_PC?? While searching code, I found these somewhere connected to 
> direct IO (bio_add_pc_page) and could find more about them]
> 
> -
> To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
> the body of a message to [EMAIL PROTECTED]
> More majordomo info at  http://vger.kernel.org/majordomo-info.html
> Please read the FAQ at  http://www.tux.org/lkml/

There was a related fix to a similar problem by Mike Christie, in resent
Kernels, If there is no chance for you working on newer kernels, than you
will have to back port it.

it is:
commit bd441deaf341c524b28fd72831ebf6fef88f1c41
Author: Mike Christie <[EMAIL PROTECTED]>
Date:   Tue Mar 13 12:52:29 2007 -0500

[SCSI] fix write buffer length in scsi_req_map_sg()

 
look it up the git trees on kernel.org

Boaz
-
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to [EMAIL PROTECTED]
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Re: Query about Bio submission / Direct IO

2007-10-22 Thread Boaz Harrosh 
On Fri, Oct 19 2007 at 8:17 +0200, Shreyansh Jain [EMAIL PROTECTED] wrote:
 Hi List,
 
 I have tried this on kernelnewbies
 http://article.gmane.org/gmane.linux.kernel.kernelnewbies/23166 but it 
 seems 
 I am not good at explaining well. trying here again.
 
 Question:
 Is there a limitation (some kind of caveat) when direct IO pages are added to 
 a bio (multiple pages per bio) and if the total length or offset of some of 
 the vectors is not aligned (PAGE_SIZE or sector size)?
 
 My scenario:
 1. I have a filesystem in which I create bio for submission to a SCSI disk 
connected in a SAN via a FC switch. 
 2. This is a direct IO request where in multiple pages are being added in a 
 bio
(bio_map_user). Also, as the user buffer I get is unaligned, I am changing
 bio's first vector offset (as well as len, bi_size accordingly).
 
 What I observe is:
 
 1. IO is performed perfectly (as expected) in case there are no SCSI failure.
end_bio gets called as expected and the user app is happy.
 2. In case I  disconnect the SCSI device from switch, my end_bio function 
keeps on getting sub-completion bio (bi_size  0 and uptodate cleared,
error set to -5).
 3. For capturing and ignoring sub-completion returns from block layer, 
using other kernel end_bio implementation as example I had a code like
 
 if(bio-bi_size  0)
return 1;
 
as the starting lines of the end_bio routine. Thus, my user space goes off 
to disk sleep and kernel log keeps on spweing messages like 
 
 ...
 Oct 17 21:56:07 mgs02 kernel: end_request: I/O error, dev sdl, sector 33639
 Oct 17 21:56:07 mgs02 kernel: sd 2:0:0:8: SCSI error: return code = 0x1
 Oct 17 21:56:07 mgs02 kernel: end_request: I/O error, dev sdl, sector 33639
 Oct 17 21:56:07 mgs02 kernel: sd 2:0:0:8: SCSI error: return code = 0x1
 Oct 17 21:56:07 mgs02 kernel: end_request: I/O error, dev sdl, sector 33639
 ...
 
 till i connect the switch back - even if that is one hour after disconnecting 
 it.
 
 Best part - it works amazingly well in case I keep the offset of the first 
 page
 aligned (somehow, at expense of corrupted data copy) - failure of SCSI disk
 (end_bio returns, bi_size=0, my code captures error) or no failure.
 
 I have tried this on 2.6.5 and 2.6.16.27 (I agree they are old, but that is 
 what I have to work  on :( ). It is a qlogic SCSI HBA. I have created the bio
  just like other kernel subsystems do.
 
 Only thing I am not sure is whether there is something special that needs to 
 be done in case of direct IO which I am missing.
 
 biodoc.txt states that:
 Note: Right now the only user of bios with more than one page is ll_rw_kio,
  which in turn means that only raw I/O uses it (direct i/o may not work right
  now).
 
 Any idea why it doesn't work (though I am expecting that this doc is 2.6
 starting era and things might have changed a lot now).
 
 Any help would be highly appreciated. Apologies if my channel of approach is
 wrong and if this post is huge (couldn't keep it shorter than this).
 
 Shreyansh
 
 
 [PS: Is this situation something to do with request flags REQ_PC /
 REQ_BLOCK_PC?? While searching code, I found these somewhere connected to 
 direct IO (bio_add_pc_page) and could find more about them]
 
 -
 To unsubscribe from this list: send the line unsubscribe linux-kernel in
 the body of a message to [EMAIL PROTECTED]
 More majordomo info at  http://vger.kernel.org/majordomo-info.html
 Please read the FAQ at  http://www.tux.org/lkml/

There was a related fix to a similar problem by Mike Christie, in resent
Kernels, If there is no chance for you working on newer kernels, than you
will have to back port it.

it is:
commit bd441deaf341c524b28fd72831ebf6fef88f1c41
Author: Mike Christie [EMAIL PROTECTED]
Date:   Tue Mar 13 12:52:29 2007 -0500

[SCSI] fix write buffer length in scsi_req_map_sg()

 
look it up the git trees on kernel.org

Boaz
-
To unsubscribe from this list: send the line unsubscribe linux-kernel in
the body of a message to [EMAIL PROTECTED]
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/

Re: Query about Bio submission / Direct IO

2007-10-22 Thread Shreyansh 
Hi list and Boaz,

On 10/22/07, Boaz Harrosh [EMAIL PROTECTED] wrote:
 On Fri, Oct 19 2007 at 8:17 +0200, Shreyansh Jain [EMAIL PROTECTED] wrote:
  Hi List,
 
---8-
  Any idea why it doesn't work (though I am expecting that this doc is 2.6
  starting era and things might have changed a lot now).
 
  Any help would be highly appreciated. Apologies if my channel of approach is
  wrong and if this post is huge (couldn't keep it shorter than this).
 
  Shreyansh
 
 
  [PS: Is this situation something to do with request flags REQ_PC /
  REQ_BLOCK_PC?? While searching code, I found these somewhere connected to
  direct IO (bio_add_pc_page) and could find more about them]
 
--8--
  -

 There was a related fix to a similar problem by Mike Christie, in resent
 Kernels, If there is no chance for you working on newer kernels, than you
 will have to back port it.

 it is:
 commit bd441deaf341c524b28fd72831ebf6fef88f1c41
 Author: Mike Christie [EMAIL PROTECTED]
 Date:   Tue Mar 13 12:52:29 2007 -0500

Thanks a lot for pointing that out to me. I will have a look at that.


 [SCSI] fix write buffer length in scsi_req_map_sg()


 look it up the git trees on kernel.org

Certainly I will do that :) ... Thanks


 Boaz


Shreyansh
-
To unsubscribe from this list: send the line unsubscribe linux-kernel in
the body of a message to [EMAIL PROTECTED]
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Please read the FAQ at  http://www.tux.org/lkml/