Re: [PATCH] util: retry open() when it gets interrupted by a signal

[Daniel P . Berrangé]

On Wed, Jul 31, 2024 at 03:25:24PM +0200, Philipp Reisner wrote:
> As with many syscalls, open() might be interrupted by a signal.
> 
> The experienced logfile entry is:
> 
> qemu-system-x86_64: -device 
> virtio-blk-pci,bus=pci.0,addr=0x7,drive=libvirt-2-format,id=virtio-disk0,bootindex=2,write-cache=on,serial=1b990c4d13b74a4e90ea:
>  Could not open '/dev/drbd1003': Interrupted system call
> 
> Retry it until it is not interrupted by a signal.

As you say, many syscalls can be interruptted by signals, so
special casing open() isn't really a solution - its just
addressing one specific instance you happened to see.

If there are certain signals that we don't want to have a
fatal interruption for, it'd be better to set SA_RESTART
with sigaction, which will auto-restart a large set of
syscalls, while allowing other signals to be fatal.

> FYI, dd has the same kind of loop aroud open().
> https://github.com/coreutils/coreutils/blob/1ae98dbda7322427e8226356fd110d2553f5fac9/src/dd.c#L1294-L1299
> 
> Signed-off-by: Philipp Reisner <philipp.reisner@linbit.com>
> ---
>  util/osdep.c | 13 ++++++++-----
>  1 file changed, 8 insertions(+), 5 deletions(-)
> 
> diff --git a/util/osdep.c b/util/osdep.c
> index 770369831b..a1269d9345 100644
> --- a/util/osdep.c
> +++ b/util/osdep.c
> @@ -294,14 +294,17 @@ bool qemu_has_direct_io(void)
>  static int qemu_open_cloexec(const char *name, int flags, mode_t mode)
>  {
>      int ret;
> +    do  {
>  #ifdef O_CLOEXEC
> -    ret = open(name, flags | O_CLOEXEC, mode);
> +        ret = open(name, flags | O_CLOEXEC, mode);
>  #else
> -    ret = open(name, flags, mode);
> -    if (ret >= 0) {
> -        qemu_set_cloexec(ret);
> -    }
> +        ret = open(name, flags, mode);
> +        if (ret >= 0) {
> +            qemu_set_cloexec(ret);
> +        }
>  #endif
> +    } while (ret == -1 && errno == EINTR);
> +
>      return ret;
>  }
>  
> -- 
> 2.45.2
> 
> 

With regards,
Daniel
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