Hi
On Thu, Nov 11, 2021 at 7:44 PM Roman Kagan <rvka...@yandex-team.ru> wrote:
> As its name suggests, ChardevClass.chr_sync_read is supposed to do a
> blocking read. The only implementation of it, tcp_chr_sync_read, does
> set the underlying io channel to the blocking mode indeed.
>
> Therefore a failure return with EAGAIN is not expected from this call.
>
> So do not retry it in qemu_chr_fe_read_all; instead place an assertion
> that it doesn't fail with EAGAIN.
>
The code was introduced in :
commit 7b0bfdf52d694c9a3a96505aa42ce3f8d63acd35
Author: Nikolay Nikolaev <n.nikol...@virtualopensystems.com>
Date: Tue May 27 15:03:48 2014 +0300
Add chardev API qemu_chr_fe_read_all
Also touched later by Daniel in:
commit 53628efbc8aa7a7ab5354d24b971f4d69452151d
Author: Daniel P. Berrangé <berra...@redhat.com>
Date: Thu Mar 31 16:29:27 2016 +0100
char: fix broken EAGAIN retry on OS-X due to errno clobbering
> Signed-off-by: Roman Kagan <rvka...@yandex-team.ru>
> ---
> chardev/char-fe.c | 7 ++-----
> 1 file changed, 2 insertions(+), 5 deletions(-)
>
> diff --git a/chardev/char-fe.c b/chardev/char-fe.c
> index 7789f7be9c..f94efe928e 100644
> --- a/chardev/char-fe.c
> +++ b/chardev/char-fe.c
> @@ -68,13 +68,10 @@ int qemu_chr_fe_read_all(CharBackend *be, uint8_t
> *buf, int len)
> }
>
> while (offset < len) {
> - retry:
> res = CHARDEV_GET_CLASS(s)->chr_sync_read(s, buf + offset,
> len - offset);
> - if (res == -1 && errno == EAGAIN) {
> - g_usleep(100);
> - goto retry;
> - }
> + /* ->chr_sync_read should block */
> + assert(!(res < 0 && errno == EAGAIN));
>
>
While I agree with the rationale to clean this code a bit, I am not so sure
about replacing it with an assert(). In the past, when we did such things
we had unexpected regressions :)
A slightly better approach perhaps is g_warn_if_fail(), although it's not
very popular in qemu.
> if (res == 0) {
> break;
> --
> 2.33.1
>
>
>
--
Marc-André Lureau
