On 20.12.19 22:15, Eric Blake wrote: > On 12/19/19 8:38 AM, Max Reitz wrote: >> fuse-export-add allows mounting block graph nodes via FUSE on some >> existing regular file. That file should then appears like a raw disk >> image, and accesses to it result in accesses to the exported BDS. >> >> Right now, we only set up the mount point and tear all mount points down >> in bdrv_close_all(). We do not implement any access functions, so >> accessing the mount point only results in errors. This will be >> addressed by a followup patch. >> >> The set of exported nodes is kept in a hash table so we can later add a >> fuse-export-remove that allows unmounting. > > Before I review this, a quick question: > > How does this compare to the recently added nbdfuse? > https://www.redhat.com/archives/libguestfs/2019-October/msg00080.html
Hm. Well, one thing is that it uses a file mount point instead of a cumbersome directory + "ramdisk" file. O:-) (Which, again, is fun because this allows you to mount a qcow2 file on itself so it appears like a raw image.) Then we get all native block layer things without needing NBD support, like resize (also growing on post-EOF writes). (It also has features the nbdfuse patch mentions are not supported there yet, i.e. fallocate() (zero writes and discards). And I don’t suppose nbdfuse supports lseek() yet either. I suppose those features could be added to nbdfuse, but, well, they are here now.) > Or put another way, maybe we get the same effect by combining qemu-nbd > with nbdfuse, but this new utility would cut out a middleman for more > efficiency, right? I would assume it has better efficiency, yes. But the performance is not very good anyway. Max
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