Messages in this thread | | | Subject | Re: writev to scsi disks | From | James Bottomley <> | Date | Wed, 20 Apr 2005 17:15:31 -0400 |
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On Wed, 2005-04-20 at 08:01 -0700, Dheeraj Pandey wrote: > I was wondering if I did a simple writev to a SCSI disk, does it take > the sg path to the device? I am guessing sg (REQ_SPECIAL) is only > true for character devices (and ioctl's) and not block devices.
? I think you misunderstand how writev works. It's design is to take a list of scattered buffers in a user program and consolidate them into a single write. This (in the current implementation) is a separate entity from the block level Scatter Gather.
If by sg write path, if you mean scatter-gather write path, then yes, that single write would be split up again into a sg list based on the device parameters if you mean does the writev sg list control where on the disk the data ends up, then no, if you use a disk device as a simple file, writev consolidates all writes to the current file position.
James
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