On Wed, Jul 31, 2024 at 03:32:52PM +0100, Peter Maydell wrote: > On Wed, 31 Jul 2024 at 15:11, Daniel P. Berrangé <berra...@redhat.com> wrote: > > > > On Wed, Jul 31, 2024 at 03:25:24PM +0200, Philipp Reisner wrote: > > > As with many syscalls, open() might be interrupted by a signal. > > > > > > The experienced logfile entry is: > > > > > > qemu-system-x86_64: -device > > > virtio-blk-pci,bus=pci.0,addr=0x7,drive=libvirt-2-format,id=virtio-disk0,bootindex=2,write-cache=on,serial=1b990c4d13b74a4e90ea: > > > Could not open '/dev/drbd1003': Interrupted system call
What is the actual signal you are seeing that impacts QEMU in this way ? > > > Retry it until it is not interrupted by a signal. > > > > As you say, many syscalls can be interruptted by signals, so > > special casing open() isn't really a solution - its just > > addressing one specific instance you happened to see. > > > > If there are certain signals that we don't want to have a > > fatal interruption for, it'd be better to set SA_RESTART > > with sigaction, which will auto-restart a large set of > > syscalls, while allowing other signals to be fatal. > > This is why we have the RETRY_ON_EINTR() macro, right? > > Currently we have some places that call qemu_open_old() inside > RETRY_ON_EINTR -- we should decide whether we want to > handle EINTR inside the qemu_open family of functions, > or make the caller deal with it, and put the macro uses > in the right place consistently. It is incredibly arbitrary where we use RETRY_ON_EINTR, which I think points towards it being a sub-optimal solution to the general problem. > > I agree that it would be nicer if we could use SA_RESTART, > but presumably there's a reason why we don't. (At any > rate code that's shared with the user-mode emulation > has to be EINTR-resistant, because we can't force the > user-mode guest code to avoid registering signal handlers > that aren't SA_RESTART.) For user mode emulation isn't it valid to just propagage the EINTR back up to the application, since EINTR is a valid errno they have to be willing to handle unless the app has itself use SA_RESTART. With regards, Daniel -- |: https://berrange.com -o- https://www.flickr.com/photos/dberrange :| |: https://libvirt.org -o- https://fstop138.berrange.com :| |: https://entangle-photo.org -o- https://www.instagram.com/dberrange :|
