On Thu, Jan 29, 2015 at 11:02:58AM +0100, Arnd Bergmann wrote: > On Wednesday 28 January 2015 18:00:25 Darrick J. Wong wrote: > > Create a new ioctl to expose the block layer's newfound ability to > > issue either a zeroing discard, a WRITE SAME with a zero page, or a > > regular write with the zero page. This BLKZEROOUT2 ioctl takes > > {start, length, flags} as parameters. So far, the only flag available > > is to enable the zeroing discard part -- without it, the call invokes > > the old BLKZEROOUT behavior. start and length have the same meaning > > as in BLKZEROOUT. > > > > Furthermore, because BLKZEROOUT2 issues commands directly to the > > storage device, we must invalidate the page cache (as a regular > > O_DIRECT write would do) to avoid returning stale cache contents at a > > later time. > > > > This patch depends on "block: Add discard flag to > > blkdev_issue_zeroout() function" in Jens' for-3.20/core branch. > > > > Signed-off-by: Darrick J. Wong <darrick.wong@xxxxxxxxxx> > > > > Would this work ok for devices that fill discarded areas with all-ones > instead of all-zeroes? I believe SD cards can do either. It won't do all-ones, because the underlying blkdev_issue_zeroout call only knows how to tell the device to write zeroes or perform a discard if the flag is set and the device is whitelisted. This patch only exposes the existing kernel call to userspace. (All-ones could be plumbed into the storage stack, but that would have to be a separate patch.) --D > > Arnd > -- > To unsubscribe from this list: send the line "unsubscribe linux-api" in > the body of a message to majordomo@xxxxxxxxxxxxxxx > More majordomo info at http://vger.kernel.org/majordomo-info.html -- To unsubscribe from this list: send the line "unsubscribe linux-fsdevel" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html