On Thu, Apr 29, 2021 at 03:41:29PM +0100, Stefan Hajnoczi wrote: > On Thu, Apr 29, 2021 at 03:22:59PM +0100, Richard W.M. Jones wrote: > > On Thu, Apr 29, 2021 at 03:05:50PM +0100, Stefan Hajnoczi wrote: > > > The purpose of this preview release is to discuss both the API design > > > and general direction of the project. API documentation is available > > > here: > > > > > > https://gitlab.com/libblkio/libblkio/-/blob/v0.1.0/docs/blkio.rst > > > > libvirt originally, and now libnbd, keep a per-thread error message > > (stored in thread-local storage). It's a lot nicer than having to > > pass &errmsg to every function. You can just write: > > > > if (nbd_connect_tcp (nbd, "remote", "nbd") == -1) { > > fprintf (stderr, > > "failed to connect to remote server: %s (errno = %d)\n", > > nbd_get_error (), nbd_get_errno ()); > > exit (EXIT_FAILURE); > > } > > > > (https://libguestfs.org/libnbd.3.html#ERROR-HANDLING) > > > > It means you can extend the range of error information available in > > future. Also you can return a 'const char *' and the application > > doesn't have to worry about lifetimes, at least in the common case. > > Thanks for sharing the idea, I think it would work well for libblkio > too. > > Do you ignore the dlclose(3) memory leak?
I believe this mechanism in libnbd ensures there is no leak in the ordinary shared library (not dlopen/dlclose) case: https://gitlab.com/nbdkit/libnbd/-/blob/f9257a9fdc68706a4079deb4ced61e1d468f28d6/lib/errors.c#L35 However I'm not sure what happens in the dlopen case, so I'm going to test that out now ... > > > Examples are available here: > > > > > > https://gitlab.com/libblkio/libblkio/-/tree/v0.1.0/examples > > > > > > The goal is to eventually include the following drivers: > > > - Linux io_uring > > > - NVMe (VFIO and vfio-user) > > > - virtio-blk (VFIO, vfio-user, vhost-user-blk, and vhost-vdpa-blk) > > > > > > There are a few reasons why libblkio is needed: > > > > > > 1. QEMU, Ceph, GlusterFS, MariaDB, and other programs have been adding > > > more low-level block I/O code, most of it duplicated. Usually only > > > one or two of Linux AIO, io_uring, userspace drivers, vhost-user > > > drivers, etc are implemented. This makes it difficult to benefit from > > > the latest advances in high-performance block I/O. > > > > > > 2. Coding to a standard API makes it possible to introduce new > > > optimizations or hardware interfaces without costly changes to the > > > software stack. > > > > > > 3. A client library is needed so applications can take advantage of > > > qemu-storage-daemon's vhost-user-blk exports. > > > > > > 4. Implementing block I/O as a library allows QEMU to use Rust for new > > > code without messy QEMU internal API bindings. Note that libblkio > > > currently does not provide a Rust crate, it only offers a C API. > > > > This is where I get confused about what this library actually does. > > It's not just a nicer wrapper around io_uring, but what is it actually > > doing? > > It's a library for what QEMU calls protocol drivers (POSIX files, > userspace NVMe driver, etc). In particular, anything offering > multi-queue block I/O fits into libblkio. > > It is not intended to replace libnbd or other network storage libraries. > libblkio's properties API is synchronous to keep things simple for > applications. Attaching to network storage needs to be asynchronous, > although the libblkio API could be extended if people want to support > network storage. I think what confuses me is why is NVMe any different from io_uring? ie would this work? $ blkio-info --output=json io_uring path=/dev/nvme0 Rich. -- Richard Jones, Virtualization Group, Red Hat http://people.redhat.com/~rjones Read my programming and virtualization blog: http://rwmj.wordpress.com virt-df lists disk usage of guests without needing to install any software inside the virtual machine. Supports Linux and Windows. http://people.redhat.com/~rjones/virt-df/
