On Tue, Sep 29, 2020 at 12:36:10PM -0500, Eric Blake wrote: > 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.
Thanks for letting me know about the bug report. The link can be added to the commit description when merging (or if I resend). Stefan
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