On Mon, Aug 10, 2020 at 03:35:55PM +0300, Denis V. Lunev wrote: > The problem this patch is trying to address is libguestfs behavior on the > appliance startup. It starts supporting to use root=UUID definition in > the kernel command line of its root filesystem using > file -- /usr/lib64/guestfs/appliance/root > This works fine with RAW image, but we are using QCOW2 as a storage to > save a bit of file space and in this case we get > QEMU QCOW Image (v3), 1610612736 bytes > instead of UUID of the root filesystem. > > The solution is very simple - we should dump first 256k of the image file > like the follows > qemu-io -c "read -V 0 256k" appliance | file - > which will provide correct result for all possible types of the appliance > storage. > > Unfortunately, additional option for qemu-io is the only and the simplest > solution as '-v' creates very specific output, which requires to be > parsed. 'qemu-img dd of=/dev/stdout' does not work and the fix would be > much more intrusive.
I like the idea of the flag - we could also use it in the nbdkit test suite. I wonder if the actual flag ('V') is a good idea because I would normally associate that with getting the version of a command. But as these are subcommand flags, that's probably not too relevant here. So I think this is fine from my point of view. Rich. > Signed-off-by: Denis V. Lunev <d...@openvz.org> > CC: Andrey Shinkevich <andrey.shinkev...@virtuozzo.com> > CC: Vladimir Sementsov-Ogievskiy <vsement...@virtuozzo.com> > CC: Kevin Wolf <kw...@redhat.com> > CC: Max Reitz <mre...@redhat.com> > CC: Richard W.M. Jones <rjo...@redhat.com> > --- > P.S. Patch to libguestfs will follow. > > qemu-io-cmds.c | 17 +++++++++++++---- > 1 file changed, 13 insertions(+), 4 deletions(-) > > diff --git a/qemu-io-cmds.c b/qemu-io-cmds.c > index baeae86d8c..7aae9726cd 100644 > --- a/qemu-io-cmds.c > +++ b/qemu-io-cmds.c > @@ -718,7 +718,7 @@ static const cmdinfo_t read_cmd = { > .cfunc = read_f, > .argmin = 2, > .argmax = -1, > - .args = "[-abCqv] [-P pattern [-s off] [-l len]] off len", > + .args = "[-abCqvV] [-P pattern [-s off] [-l len]] off len", > .oneline = "reads a number of bytes at a specified offset", > .help = read_help, > }; > @@ -728,6 +728,7 @@ static int read_f(BlockBackend *blk, int argc, char > **argv) > struct timespec t1, t2; > bool Cflag = false, qflag = false, vflag = false; > bool Pflag = false, sflag = false, lflag = false, bflag = false; > + bool vrawflag = true; > int c, cnt, ret; > char *buf; > int64_t offset; > @@ -737,7 +738,7 @@ static int read_f(BlockBackend *blk, int argc, char > **argv) > int pattern = 0; > int64_t pattern_offset = 0, pattern_count = 0; > > - while ((c = getopt(argc, argv, "bCl:pP:qs:v")) != -1) { > + while ((c = getopt(argc, argv, "bCl:pP:qs:vV")) != -1) { > switch (c) { > case 'b': > bflag = true; > @@ -777,6 +778,9 @@ static int read_f(BlockBackend *blk, int argc, char > **argv) > case 'v': > vflag = true; > break; > + case 'V': > + vrawflag = true; > + break; > default: > qemuio_command_usage(&read_cmd); > return -EINVAL; > @@ -869,10 +873,15 @@ static int read_f(BlockBackend *blk, int argc, char > **argv) > if (vflag) { > dump_buffer(buf, offset, count); > } > + if (vrawflag) { > + write(STDOUT_FILENO, buf, count); > + } > > /* Finally, report back -- -C gives a parsable format */ > - t2 = tsub(t2, t1); > - print_report("read", &t2, offset, count, total, cnt, Cflag); > + if (!vrawflag) { > + t2 = tsub(t2, t1); > + print_report("read", &t2, offset, count, total, cnt, Cflag); > + } > > out: > qemu_io_free(buf); > -- > 2.17.1 -- Richard Jones, Virtualization Group, Red Hat http://people.redhat.com/~rjones Read my programming and virtualization blog: http://rwmj.wordpress.com virt-p2v converts physical machines to virtual machines. Boot with a live CD or over the network (PXE) and turn machines into KVM guests. http://libguestfs.org/virt-v2v