Hi Block developers, I would like to add a feature to Qemu to drain all traffic from a block so that I can take external snaphosts without the risk to that in the middle of a write operation. Its meant for cases where where QGA freeze/thaw is not available.
For me its enough to have this through qemu-io, but Kevin asked me to check if its not worth to have a stable API for it and present it via QMP/HMP. What are your thoughts? Thanks, Peter --- qemu-io-cmds.c | 78 ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 78 insertions(+) diff --git a/qemu-io-cmds.c b/qemu-io-cmds.c index 312fc6d..49d82fe 100644 --- a/qemu-io-cmds.c +++ b/qemu-io-cmds.c @@ -1565,6 +1565,82 @@ static const cmdinfo_t flush_cmd = { .oneline = "flush all in-core file state to disk", }; +static const cmdinfo_t drain_cmd; + +static int drain_f(BlockBackend *blk, int argc, char **argv) +{ + BlockDriverState *bs = blk_bs(blk); + bool flush = false; + int c; + + while ((c = getopt(argc, argv, "f")) != -1) { + switch (c) { + case 'f': + flush = true; + break; + default: + return qemuio_command_usage(&drain_cmd); + } + } + + if (optind != argc) { + return qemuio_command_usage(&drain_cmd); + } + + + if (bs->quiesce_counter) { + printf("drain failed: device is already drained!\n"); + return 1; + } + + bdrv_drained_begin(bs); /* complete I/O */ + if (flush) { + bdrv_flush(bs); + bdrv_drain(bs); /* in case flush left pending I/O */ + printf("flushed all pending I/O\n"); + } + printf("drain successful\n"); + return 0; +} + +static void drain_help(void) +{ + printf( +"\n" +" Drains all external I/O from the device\n" +"\n" +" -f, -- flush all in-core file state to disk\n" +"\n"); +} + +static const cmdinfo_t drain_cmd = { + .name = "drain", + .cfunc = drain_f, + .args = "[-f]", + .argmin = 0, + .argmax = -1, + .oneline = "cease to send I/O to the device", + .help = drain_help +}; + +static int undrain_f(BlockBackend *blk, int argc, char **argv) +{ + BlockDriverState *bs = blk_bs(blk); + if (!bs->quiesce_counter) { + printf("undrain failed: device is not drained!\n"); + return 1; + } + bdrv_drained_end(bs); + printf("undrain successful\n"); + return 0; +} + +static const cmdinfo_t undrain_cmd = { + .name = "undrain", + .cfunc = undrain_f, + .oneline = "continue I/O to a drained device", +}; + static int truncate_f(BlockBackend *blk, int argc, char **argv) { int64_t offset; @@ -2296,6 +2372,8 @@ static void __attribute((constructor)) init_qemuio_commands(void) qemuio_add_command(&aio_write_cmd); qemuio_add_command(&aio_flush_cmd); qemuio_add_command(&flush_cmd); + qemuio_add_command(&drain_cmd); + qemuio_add_command(&undrain_cmd); qemuio_add_command(&truncate_cmd); qemuio_add_command(&length_cmd); qemuio_add_command(&info_cmd); -- 1.9.1