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/
