linux-kernel - Re: [PATCH v1] tools/hv: terminate fcopy daemon if read from uio fails

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Message-ID: <20241028090620.GA32655@linuxonhyperv3.guj3yctzbm1etfxqx2vob5hsef.xx.internal.cloudapp.net>
Date: Mon, 28 Oct 2024 02:06:20 -0700
From: Saurabh Singh Sengar <ssengar@...ux.microsoft.com>
To: Olaf Hering <olaf@...fle.de>
Cc: linux-hyperv@...r.kernel.org, linux-kernel@...r.kernel.org,
	"K. Y. Srinivasan" <kys@...rosoft.com>,
	Haiyang Zhang <haiyangz@...rosoft.com>,
	Wei Liu <wei.liu@...nel.org>, Dexuan Cui <decui@...rosoft.com>
Subject: Re: [PATCH v1] tools/hv: terminate fcopy daemon if read from uio
 fails

On Fri, Oct 25, 2024 at 04:28:27PM +0200, Olaf Hering wrote:
> Terminate endless loop in reading fails, to avoid flooding syslog.
> 
> This happens if the "Guest services" integration service is
> disabled at runtime in the VM settings.
> 
> Also handle an interrupted system call, and continue in this case.
> 
> Signed-off-by: Olaf Hering <olaf@...fle.de>
> ---
> 
> A more complete fix is to handle this properly in the kernel,
> by making the file descriptor unavailable for further operations.
> 
>  tools/hv/hv_fcopy_uio_daemon.c | 4 +++-
>  1 file changed, 3 insertions(+), 1 deletion(-)
> 
> diff --git a/tools/hv/hv_fcopy_uio_daemon.c b/tools/hv/hv_fcopy_uio_daemon.c
> index 7a00f3066a98..281fd95dc0d8 100644
> --- a/tools/hv/hv_fcopy_uio_daemon.c
> +++ b/tools/hv/hv_fcopy_uio_daemon.c
> @@ -468,8 +468,10 @@ int main(int argc, char *argv[])
>  		 */
>  		ret = pread(fcopy_fd, &tmp, sizeof(int), 0);
>  		if (ret < 0) {
> +			if (errno == EINTR || errno == EAGAIN)
> +				continue;
>  			syslog(LOG_ERR, "pread failed: %s", strerror(errno));

Thanks for the patch. Changes look good to me, I will suggest to improve this
log message incase the error type is EIO by suggesting that users verify if
'Guest Services' is enabled.

- Saurabh