Re: [RFC PATCH 6/6] block: Add a thread-pool version of fstat

[Eric Blake]

On Tue, May 23, 2023 at 06:39:03PM -0300, Fabiano Rosas wrote:
> From: João Silva <jsilva@suse.de>
> 
> The fstat call can take a long time to finish when running over
> NFS. Add a version of it that runs in the thread pool.
> 
> Adapt one of its users, raw_co_get_allocated_file size to use the new
> version. That function is called via QMP under the qemu_global_mutex
> so it has a large chance of blocking VCPU threads in case it takes too
> long to finish.
> 
> Signed-off-by: João Silva <jsilva@suse.de>
> Signed-off-by: Fabiano Rosas <farosas@suse.de>
> ---
>  block/file-posix.c      | 40 +++++++++++++++++++++++++++++++++++++---
>  include/block/raw-aio.h |  4 +++-
>  2 files changed, 40 insertions(+), 4 deletions(-)

Should this change occur earlier in the series, before calling
commands are marked with QAPI coroutine flags?  Otherwise, you have a
bisection bug, where something marked coroutine can end up hanging
when it calls a blocking syscall in the wrong context without the help
of this patch offloading the syscall into a helper thread.

-- 
Eric Blake, Principal Software Engineer
Red Hat, Inc.           +1-919-301-3266
Virtualization:  qemu.org | libvirt.org