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

[Blue Swirl]

On Wed, Apr 17, 2013 at 9:46 AM, Paolo Bonzini <address@hidden> wrote:
> 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.
>
> Reviewed-by: Juan Quintela <address@hidden>
> Reviewed-by: Orit Wassermann <address@hidden>
> Signed-off-by: Paolo Bonzini <address@hidden>
> ---
>  savevm.c | 101 
> ++++++++++++++++++++++++++++++++++++++++++++++++++++++++-------
>  1 file changed, 90 insertions(+), 11 deletions(-)
>
> diff --git a/savevm.c b/savevm.c
> index ffabbff..31dcce9 100644
> --- a/savevm.c
> +++ b/savevm.c
> @@ -356,9 +356,94 @@ static const QEMUFileOps stdio_file_write_ops = {
>      .close =      stdio_fclose
>  };
>
> +static ssize_t unix_writev_buffer(void *opaque, struct iovec *iov, int 
> iovcnt,
> +                                  int64_t pos)
> +{
> +    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);

This breaks mingw32 build:
  LINK  i386-softmmu/qemu-system-i386.exe
savevm.o: In function `unix_writev_buffer':
/src/qemu/savevm.c:382: undefined reference to `_writev'
collect2: error: ld returned 1 exit status

> +        } 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 +452,15 @@ 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
>
>