Am 03.07.2018 um 16:48 hat Ari Sundholm geschrieben: > This patch series adds a new block driver, blklogwrites, to QEMU. The > driver is given two block devices: a raw device backed by an image or a > host block device, and a log device, typically backed by a file, on > which writes to the raw device are logged. > > The logging format used is the same as in the dm-log-writes target of > the Linux kernel device mapper. The log reflects the writes that have > been performed on the guest block device and flushed. To be strict, the > log may contain writes that have not been flushed yet, but they are > technically outside the bounds of the log until the next flush updates > the metadata in the log superblock. We believe these semantics to be > useful even though they may not be completely identical to those of > dm-log-writes. > > This functionality can be used for crash consistency and fs consistency > testing in filesystem drivers, including on non-Linux guests and older > guests running Linux versions without support for dm-log-writes. This > is simple and useful. Admittedly this and more advanced things could > perhaps be done by extending the quorum driver, but this approach would > require re-engineering the functionality and involve a more complicated > setup, so we offer this simple solution which we have found useful > internally. > > In the first patch of this series, two block permission constants are > moved from block.c to include/block/block.h to make them available > outside of block.c. The next patch uses these constants. > > In the second patch, the blklogwrites driver is introduced. The driver > accepts a target block device to be logged, a log device and an option > to set the sector size used for logging. All requests are aligned to > this sector size, and offsets and sizes in the log entries will be > expressed as a multiple of this value.
Thanks, applied to the block branch. Kevin
