On Thu, Sep 15, 2016 at 12:46:07PM +0100, Alex Bligh wrote: > Essentially NBD does supports FLUSH/FUA like this: > > https://www.kernel.org/doc/Documentation/block/writeback_cache_control.txt > > IE supports the same FLUSH/FUA primitives as other block drivers (AIUI). > > Link to protocol (per last email) here: > > https://github.com/yoe/nbd/blob/master/doc/proto.md#ordering-of-messages-and-writes Flush as defined by the Linux block layer (and supported that way in SCSI, ATA, NVMe) only requires to flush all already completed writes to non-volatile media. It does not impose any ordering unlike the nbd spec. FUA as defined by the Linux block layer (and supported that way in SCSI, ATA, NVMe) only requires the write operation the FUA bit is set on to be on non-volatile media before completing the write operation. It does not impose any ordering, which seems to match the nbd spec. Unlike the NBD spec Linux does not allow FUA to be set on anything by WRITE commands. Some other storage protocols allow a FUA bit on READ commands or other commands that write data to the device, though. -- To unsubscribe from this list: send the line "unsubscribe linux-block" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
