On 9/29/20 7:55 AM, Stefan Hajnoczi wrote: > Block exports are used by softmmu, qemu-storage-daemon, and qemu-nbd. > They are not used by other programs and are not otherwise needed in > libblock. > > Undo the recent move of blockdev-nbd.c from blockdev_ss into block_ss. > Since bdrv_close_all() (libblock) calls blk_exp_close_all() > (libblockdev) a stub function is required.. > > Make qemu-ndb.c use signal handling utility functions instead of > duplicating the code. This helps because os-posix.c is in libblockdev > and it depends on a qemu_system_killed() symbol that qemu-nbd.c lacks. > Once we use the signal handling utility functions we also end up > providing the necessary symbol.
Hmm. I just stumbled on a long-standing bug in qemu-nbd - it installs a SIGTERM handler, but not a SIGINT or SIGHUP handler. This matters in the following sequence: qemu-nbd -f qcow2 -B bitmap image # Ctrl-C qemu-nbd -f qcow2 -B bitmap image because the first instance dies with SIGINT but there is no handler installed, qemu-nbd does not release the bitmap from being marked in-use, and the second instance then fails with: qemu-nbd: Bitmap 'b0' is inconsistent and cannot be used And to my surprise, while I was trying to find the root cause to fixing the bug I just found, I noticed that your patch happens to fix that... > +++ b/qemu-nbd.c > @@ -581,20 +586,12 @@ int main(int argc, char **argv) > const char *pid_file_name = NULL; > BlockExportOptions *export_opts; > > + os_setup_early_signal_handling(); > + > #if HAVE_NBD_DEVICE > - /* The client thread uses SIGTERM to interrupt the server. A signal > - * handler ensures that "qemu-nbd -v -c" exits with a nice status code. > - */ > - struct sigaction sa_sigterm; > - memset(&sa_sigterm, 0, sizeof(sa_sigterm)); > - sa_sigterm.sa_handler = termsig_handler; > - sigaction(SIGTERM, &sa_sigterm, NULL); > + os_setup_signal_handling(); ...by installing a SIGINT handler. Is HAVE_NBD_DEVICE really the best gate for this code, or is it really whether we are compiling for mingw? At any rate, you may want to add a link to https://bugzilla.redhat.com/show_bug.cgi?id=1883608 in the commit message, and/or separate the bug fix out into a separate commit. -- Eric Blake, Principal Software Engineer Red Hat, Inc. +1-919-301-3226 Virtualization: qemu.org | libvirt.org
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