Messages in this thread | | | Date | Wed, 21 Jul 2004 17:00:07 -0700 | From | Shesha Sreenivasamurthy <> | Subject | Re: O_DIRECT |
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You are right I am not using any file system. Just did that experiment by creating FS too. That also did not help. I shared that information. You are absolutely right I am dealing with straight partitions.
(1) With staraight partition even if I explicitly set the block size to 4096 and adher to the rules of O_DIRECT i cannot read/write
(2) With staraight partition if I set the block size to 1024 and adher to the rules of O_DIRECT i can read/write
Ruls include : Alligning the buffer & read/write multiple of block size.
-Shesha
Rob van Nieuwkerk wrote:
>On Wed, 21 Jul 2004 16:18:37 -0700 >Shesha Sreenivasamurthy <shesha@inostor.com> wrote: > >Hi Shesha, > >Your original question (and my answer) was about a different situation: > > - partition with no filesystem > - access on this raw partition > >Now you start talking about various file-systems and I get the impression >that you access the device through the file-system (although that is >not very clear in your text) on a mounted fs. > >What I told you applied to straight partitions (without mounted a mounted fs). > >I don't know the exact rules for the various file-systems. >They might be different (and some might not support O_DIRECT at all). >I expect the same "soft block size rules" to apply for the filesystems >that *do* support O_DIRECT. Note that mounting a partition might >change the softblock size of that partition used by the kernel from thereon. > > > greetings, > Rob van Nieuwkerk > >PS1: what kernel are you using ? > >PS2: what are you trying to do ? > >PS3: you mention "our driver ..". What is this driver ? > > > > > >>I could never get it working with 4096 block size. >> >>I created an EXT3 with blockize=4096 (mkfs.ext3 -b 4096 /dev/sda11). >>Alligned memory to 4096 boundary. Read 8192 Bytes. -> UNSUCCESSFUL :( >>I created an XFS with blockize=4096 (mkfs.xfs -f -b size=4096 >>/dev/sda11). Alligned memory to 4096 boundary. Read 8192 Bytes. -> >>UNSUCCESSFUL :( >> >>SUCCESS HAPPEND ONLY WHEN .... >> >>1. I created an XFS with blockize=4096 (mkfs.xfs -f -b size=4096 >>/dev/sda11). >> OR >> I created an EXT3 with blockize=4096 (mkfs.ext3 -b 4096 /dev/sda11). >> >>2. Changed blocksizeto 1024 >>3. Alligned memory to 1024 boundary. >>4 Read 8192 Bytes. -> SUCCESSFUL :) >> >>-Shesha >> >> >>Rob van Nieuwkerk wrote: >> >> >> >>>On Wed, 21 Jul 2004 11:01:20 -0700 >>>Shesha Sreenivasamurthy <shesha@inostor.com> wrote: >>> >>>Hi Shesha, >>> >>> >>> >>> >>> >>>>ohhh OK, if the block size is 4096, then the read/write size must be >>>>integer multiple of 4096 ??? is it ??? >>>>In general should the read/write length be a multiple of block size? >>>> >>>> >>>> >>>> >>>Yes, see my previous emails. >>> >>> greetings, >>> Rob van Nieuwkerk >>> >>> >>> >>> >>> >>>>Rob van Nieuwkerk wrote: >>>> >>>> >>>> >>>> >>>> >>>>>On Wed, 21 Jul 2004 10:10:26 -0700 >>>>>Shesha Sreenivasamurthy <shesha@inostor.com> wrote: >>>>> >>>>>Hi Shesha, >>>>> >>>>>You don't mention what the *size* of your read()/write() is. >>>>>Besides a requirement on the alignment of the read/write buffer >>>>>the size of the read()/write() must also be OK. >>>>> >>>>> greetings, >>>>> Rob van Nieuwkerk >>>>> >>>>> >>>>> >>>>> >>>>> >>>>> >>>>> >>>>>>This is what I found .... >>>>>> >>>>>>Our driver sets the block size to be 4096. so BLKBSZGET will return >>>>>>4096. So if I allin the memory at 4096 boundary, I cannot read using >>>>>>O_DIRECT. But, if I set the block size to 512. I can read/write >>>>>>successfully. It also works with 1024, but no with 4096 >>>>>> >>>>>>So the recepie what I am following is ... >>>>>> >>>>>>BLKBSZGET -> Get original block size >>>>>>BLKBSZSET -> Set the block size to 512 >>>>>>READ | WRITE Successfully ;) >>>>>>BLKBSZSET -> Set back to the original block size >>>>>> >>>>>>-Shesha >>>>>> >>>>>>Rob van Nieuwkerk wrote: >>>>>> >>>>>> >>>>>> >>>>>> >>>>>> >>>>>> >>>>>> >>>>>>>On Tue, 20 Jul 2004 10:27:57 -0700 >>>>>>>Shesha Sreenivasamurthy <shesha@inostor.com> wrote: >>>>>>> >>>>>>>Hi Shesha, >>>>>>> >>>>>>> >>>>>>> >>>>>>> >>>>>>> >>>>>>> >>>>>>> >>>>>>> >>>>>>> >>>>>>>>I am having trouble with O_DIRECT. Trying to read or write from a block >>>>>>>>device partition. >>>>>>>> >>>>>>>>1. Can O_DIRECT be used on a plain block device partition say >>>>>>>>"/dev/sda11" without having a filesystem on it. >>>>>>>> >>>>>>>> >>>>>>>> >>>>>>>> >>>>>>>> >>>>>>>> >>>>>>>> >>>>>>>> >>>>>>>yes. >>>>>>> >>>>>>> >>>>>>> >>>>>>> >>>>>>> >>>>>>> >>>>>>> >>>>>>> >>>>>>> >>>>>>>>2. If no file system is created then what should be the softblock size. >>>>>>>>I am using the IOCTL "BLKBSZGET". Is this correct? >>>>>>>> >>>>>>>> >>>>>>>> >>>>>>>> >>>>>>>> >>>>>>>> >>>>>>>> >>>>>>>> >>>>>>>yes. >>>>>>> >>>>>>> >>>>>>> >>>>>>> >>>>>>> >>>>>>> >>>>>>> >>>>>>> >>>>>>> >>>>>>>>3. Can we use SEEK_END with O_DIRECT on a partition without filesystem. >>>>>>>> >>>>>>>> >>>>>>>> >>>>>>>> >>>>>>>> >>>>>>>> >>>>>>>> >>>>>>>> >>>>>>>yes. >>>>>>> >>>>>>>I'm using these exact things in an application. >>>>>>> >>>>>>>Note that with 2.4 kernels the "granularity" you can use for offset >>>>>>>and r/w size is the softblock size (*). For 2.6 the requirements are >>>>>>>much more relaxed: it's the device blocksize (typically 512 byte). >>>>>>> >>>>>>>(*): actually one of offset or r/w size has a smaller minimum if >>>>>>>I remember correctly. Don't remember which one. But if you assume >>>>>>>the softblock size as a minimum for both you're allways safe. >>>>>>> >>>>>>> greetings, >>>>>>> Rob van Nieuwkerk >>>>>>> >>>>>>>-- >>>>>>>Kernelnewbies: Help each other learn about the Linux kernel. >>>>>>>Archive: http://mail.nl.linux.org/kernelnewbies/ >>>>>>>FAQ: http://kernelnewbies.org/faq/ >>>>>>> >>>>>>> >>>>>>>. >>>>>>> >>>>>>> >>>>>>> >>>>>>> >>>>>>> >>>>>>> >>>>>>> >>>>>>> >>>>>>> >>>>>-- >>>>>Kernelnewbies: Help each other learn about the Linux kernel. >>>>>Archive: http://mail.nl.linux.org/kernelnewbies/ >>>>>FAQ: http://kernelnewbies.org/faq/ >>>>> >>>>> >>>>>. >>>>> >>>>> >>>>> >>>>> >>>>> >>>>> >>>>> >>>-- >>>Kernelnewbies: Help each other learn about the Linux kernel. >>>Archive: http://mail.nl.linux.org/kernelnewbies/ >>>FAQ: http://kernelnewbies.org/faq/ >>> >>> >>>. >>> >>> >>> >>> >>> > >. > > >
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