Messages in this thread | | | Date | Thu, 8 May 1997 10:18:46 +0100 (GMT/BST) | From | Mike Jagdis <> | Subject | Re: Raw devices (Was:Re: NTFS, FAT32, etc.) |
| |
On Thu, 8 May 1997, Martin von Loewis wrote:
> >From looking at fs/block_dev.c, I understand that opening a block > device with O_SYNC does indeed give you unbuffered devices. If this is > the case, why is everybody claiming Linux does not support it?
O_SYNC on a block device simply means that a write won't return until the data has been written to the device. It still goes through the buffer cache and you still have to copy the data between user memory and the buffer cache.
What heavy iron databases seem to want is the ability to schedule all their own I/O using AIO in blocksized buffers with the kernel side doing the I/O direct to/from the given buffer in user space. No buffer copying. No kernel memory wasted in buffering. No read ahead other than that specifically done by the program.
Mike
-- .----------------------------------------------------------------------. | Mike Jagdis | Internet: mailto:mike@roan.co.uk | | Roan Technology Ltd. | | | 54A Peach Street, Wokingham | Telephone: +44 118 989 0403 | | RG40 1XG, ENGLAND | Fax: +44 118 989 1195 | `----------------------------------------------------------------------'
| |