(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@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
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