Re: [Qemu-devel] [PATCH] exec-migration: handle EINTR in popen_get_buffer()

[Michael S. Tsirkin]

On Mon, Jun 08, 2009 at 07:27:21PM +0300, Uri Lublin wrote:
> Sometimes, upon interrupt, fread returns with no data, and
> the (incoming exec) migration fails.
> 
> Fix by retrying on such a case.
> 
> Signed-off-by: Uri Lublin <address@hidden>
> ---
>  savevm.c |    9 ++++++++-
>  1 files changed, 8 insertions(+), 1 deletions(-)
> 
> diff --git a/savevm.c b/savevm.c
> index 248aea3..df2486d 100644
> --- a/savevm.c
> +++ b/savevm.c
> @@ -215,7 +215,14 @@ static int popen_put_buffer(void *opaque, const uint8_t 
> *buf, int64_t pos, int s
>  static int popen_get_buffer(void *opaque, uint8_t *buf, int64_t pos, int 
> size)
>  {
>      QEMUFilePopen *s = opaque;
> -    return fread(buf, 1, size, s->popen_file);
> +    FILE *fp = s->popen_file;
> +    int bytes;
> +
> +    do {
> +        clearerr(fp);

Would it make sense to only clearerr on EINTR - if we intend to retry?

> +        bytes = fread(buf, 1, size, fp);
> +    } while ((bytes == 0) && ferror(fp) && (errno == EINTR));


This does nothing about partial reads (bytes != 0)
I think it's intentional because the user actually retries
partial reads. Right?
 
> +    return bytes;
>  }
> 
>  static int popen_close(void *opaque)

Looking at qemu_fill_buffer, it seems that it is enough to set
bytes to -EAGAIN. User will then retry. Correct?

-- 
MST