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/ > >>> > >>> > >>>. > >>> > >>> > >>> > >>> > >>> > > > >-- > >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/
