On Wed, May 15, 2019 at 10:57:57PM -0500, Eric Blake wrote:
It's easy to expose new callbacks to sh plugins, by borrowing tri-state code from can_fua. It's possible that nbdkit emulate will actually work well (in our example.sh script, the kernel caching a pread from one dd invocation may indeed speed up the next access), but for the sake of the example, I demonstrated advertising a no-op handler.
The shell plugin, coupled with Rich's work on libnbd as a client-side library for actually exercising calls to NBD_CMD_CACHE, will be a useful way to prove that cache commands even make it through the stack. (Remember, qemu 3.0 was released with a fatally flawed NBD_CMD_CACHE server implementation, because there were no open source clients at the time that could actually send the command to test the server with).
Signed-off-by: Eric Blake <eblake@redhat.com> --- plugins/sh/nbdkit-sh-plugin.pod | 27 ++++++++--- plugins/sh/sh.c | 81 +++++++++++++++++++++++++++++++++ plugins/sh/example.sh | 7 +++ 3 files changed, 109 insertions(+), 6 deletions(-)
diff --git a/plugins/sh/nbdkit-sh-plugin.pod b/plugins/sh/nbdkit-sh-plugin.pod index 8af88b4..39b99a2 100644 --- a/plugins/sh/nbdkit-sh-plugin.pod +++ b/plugins/sh/nbdkit-sh-plugin.pod @@ -220,7 +220,7 @@ This method is required.
Unlike in other languages, you B<must> provide the C<can_*> methods otherwise they are assumed to all return false and your C<pwrite>, -C<flush>, C<trim>, C<zero> and C<extents> methods will never be +C<flush>, C<trim>, C<zero>, and C<extents> methods will never be
I wonder if you meant to add C<cache> to this sentence? Rich. -- Richard Jones, Virtualization Group, Red Hat http://people.redhat.com/~rjones Read my programming and virtualization blog: http://rwmj.wordpress.com virt-p2v converts physical machines to virtual machines. Boot with a live CD or over the network (PXE) and turn machines into KVM guests. http://libguestfs.org/virt-v2v