On Wed, 21 Jul 2004 16:18:37 -0700
Shesha Sreenivasamurthy <shesha@xxxxxxxxxxx> 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@xxxxxxxxxxx> 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@xxxxxxxxxxx> 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@xxxxxxxxxxx> 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.
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> >>>>>FAQ: http://kernelnewbies.org/faq/
> >>>>>
> >>>>>
> >>>>>.
> >>>>>
> >>>>>
> >>>>>
> >>>>>
> >>>>>
> >>>>>
> >>>>>
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> >>>Archive: http://mail.nl.linux.org/kernelnewbies/
> >>>FAQ: http://kernelnewbies.org/faq/
> >>>
> >>>
> >>>.
> >>>
> >>>
> >>>
> >>>
> >>>
> >
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> >
> >
> >
>
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