[Libguestfs] FYI: nbdfuse support for trim and writing zeroes

I added support for trimming to nbdfuse over the weekend: https://gitlab.com/nbdkit/libnbd/-/commit/800c021f39ddfa1dd40d8dcc8645463... This intercepts Linux fallocate(2) on the file and if the mode parameter contains FALLOC_FL_PUNCH_HOLE then it will punch a hole using nbd_trim. This all appears to work fine. As noted in the above commit, in theory we could also check for mode & FALLOC_FL_ZERO_RANGE. When I use "fallocate -z ..." on a file, I see this is the mode parameter being passed to the system call: fallocate(3, FALLOC_FL_ZERO_RANGE, 512, 512) = 0 However it appears as if the fuse kernel module doesn't pass the flag through to nbdfuse. (I checked the kernel code too, and that *seems* to agree with my assessment). So for now I left support for zeroing in there but disabled the test. The fuse developer mailing list seems to be mostly spam. There is this closed github issue which says to contact the kernel developers which I have not done: https://github.com/libfuse/libfuse/issues/395 Next step for nbdfuse is to add multithreading support which would greatly improve performance but is rather complicated to implement. Rich. -- Richard Jones, Virtualization Group, Red Hat http://people.redhat.com/~rjones Read my programming and virtualization blog: http://rwmj.wordpress.com virt-top is 'top' for virtual machines. Tiny program with many powerful monitoring features, net stats, disk stats, logging, etc. http://people.redhat.com/~rjones/virt-top