Thank you very much .... -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. Archive: http://mail.nl.linux.org/kernelnewbies/ FAQ: http://kernelnewbies.org/faq/
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-- 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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-- 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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-- Kernelnewbies: Help each other learn about the Linux kernel. Archive: http://mail.nl.linux.org/kernelnewbies/ FAQ: http://kernelnewbies.org/faq/
