Re: [Qemu-devel] [PATCH 6/6] qemu-file: do not use stdio for qemu_fdopen

[Anthony Liguori <anthony@codemonkey.ws>]

Paolo Bonzini <pbonzini@redhat.com> writes:

> This uses system calls directly for Unix file descriptors, so that the
> efficient writev_buffer can be used.  Pay attention to the possibility
> of partial writes in writev.
>
> Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

Needs rebasing:

  CC    i386-softmmu/savevm.o
/home/aliguori/git/qemu/savevm.c:439:5: error: initialization from incompatible pointer type [-Werror]
/home/aliguori/git/qemu/savevm.c:439:5: error: (near initialization for ‘unix_write_ops.writev_buffer’) [-Werror]
cc1: all warnings being treated as errors
make[1]: *** [savevm.o] Error 1
make: *** [subdir-i386-softmmu] Error 2
d13ed415c0ab9f7cf29226022f8c24d1b8dc794d is the first bad commit
commit d13ed415c0ab9f7cf29226022f8c24d1b8dc794d
Author: Paolo Bonzini <pbonzini@redhat.com>
Date:   Wed Mar 27 17:36:32 2013 +0100

    qemu-file: do not use stdio for qemu_fdopen

Regards,

Anthony Liguori

> ---
>  savevm.c | 100 ++++++++++++++++++++++++++++++++++++++++++++++++++++++++-------
>  1 file changed, 89 insertions(+), 11 deletions(-)
>
> diff --git a/savevm.c b/savevm.c
> index 0415830..8eb5aab 100644
> --- a/savevm.c
> +++ b/savevm.c
> @@ -356,9 +356,93 @@ static const QEMUFileOps stdio_file_write_ops = {
>      .close =      stdio_fclose
>  };
>  
> +static ssize_t unix_writev_buffer(void *opaque, struct iovec *iov, int iovcnt)
> +{
> +    QEMUFileSocket *s = opaque;
> +    ssize_t len, offset;
> +    ssize_t size = iov_size(iov, iovcnt);
> +    ssize_t total = 0;
> +
> +    assert(iovcnt > 0);
> +    offset = 0;
> +    while (size > 0) {
> +        /* Find the next start position; skip all full-sized vector elements  */
> +        while (offset >= iov[0].iov_len) {
> +            offset -= iov[0].iov_len;
> +            iov++, iovcnt--;
> +        }
> +
> +        /* skip `offset' bytes from the (now) first element, undo it on exit */
> +        assert(iovcnt > 0);
> +        iov[0].iov_base += offset;
> +        iov[0].iov_len -= offset;
> +
> +        do {
> +            len = writev(s->fd, iov, iovcnt);
> +        } while (len == -1 && errno == EINTR);
> +        if (len == -1) {
> +            return -errno;
> +        }
> +
> +        /* Undo the changes above */
> +        iov[0].iov_base -= offset;
> +        iov[0].iov_len += offset;
> +
> +        /* Prepare for the next iteration */
> +        offset += len;
> +        total += len;
> +        size -= len;
> +    }
> +
> +    return total;
> +}
> +
> +static int unix_get_buffer(void *opaque, uint8_t *buf, int64_t pos, int size)
> +{
> +    QEMUFileSocket *s = opaque;
> +    ssize_t len;
> +
> +    for (;;) {
> +        len = read(s->fd, buf, size);
> +        if (len != -1) {
> +            break;
> +        }
> +        if (errno == EAGAIN) {
> +            yield_until_fd_readable(s->fd);
> +        } else if (errno != EINTR) {
> +            break;
> +        }
> +    }
> +
> +    if (len == -1) {
> +        len = -errno;
> +    }
> +    return len;
> +}
> +
> +static int unix_close(void *opaque)
> +{
> +    QEMUFileSocket *s = opaque;
> +    close(s->fd);
> +    g_free(s);
> +    return 0;
> +}
> +
> +static const QEMUFileOps unix_read_ops = {
> +    .get_fd =     socket_get_fd,
> +    .get_buffer = unix_get_buffer,
> +    .close =      unix_close
> +};
> +
> +static const QEMUFileOps unix_write_ops = {
> +    .get_fd =     socket_get_fd,
> +    .writev_buffer = unix_writev_buffer,
> +    .close =      unix_close
> +};
> +
>  QEMUFile *qemu_fdopen(int fd, const char *mode)
>  {
> -    QEMUFileStdio *s;
> +    QEMUFileSocket *s;
>  
>      if (mode == NULL ||
>  	(mode[0] != 'r' && mode[0] != 'w') ||
> @@ -367,21 +451,15 @@ QEMUFile *qemu_fdopen(int fd, const char *mode)
>          return NULL;
>      }
>  
> -    s = g_malloc0(sizeof(QEMUFileStdio));
> -    s->stdio_file = fdopen(fd, mode);
> -    if (!s->stdio_file)
> -        goto fail;
> +    s = g_malloc0(sizeof(QEMUFileSocket));
> +    s->fd = fd;
>  
>      if(mode[0] == 'r') {
> -        s->file = qemu_fopen_ops(s, &stdio_file_read_ops);
> +        s->file = qemu_fopen_ops(s, &unix_read_ops);
>      } else {
> -        s->file = qemu_fopen_ops(s, &stdio_file_write_ops);
> +        s->file = qemu_fopen_ops(s, &unix_write_ops);
>      }
>      return s->file;
> -
> -fail:
> -    g_free(s);
> -    return NULL;
>  }
>  
>  static const QEMUFileOps socket_read_ops = {
> -- 
> 1.8.1.4