Re: [PATCH v2 18/21] migration: remove the QEMUFileOps 'get_buffer' callback

["Dr. David Alan Gilbert" <dgilbert@redhat.com>]

* Daniel P. Berrangé (berrange@redhat.com) wrote:
> This directly implements the get_buffer logic using QIOChannel APIs.
> 
> Reviewed-by: Dr. David Alan Gilbert <dgilbert@redhat.com>
> Signed-off-by: Daniel P. Berrangé <berrange@redhat.com>

Coverity is pointing out a fun deadcode path from this:

> diff --git a/migration/qemu-file.c b/migration/qemu-file.c
> index 5eb8cf0e28..df438724cd 100644
> --- a/migration/qemu-file.c
> +++ b/migration/qemu-file.c
> @@ -377,8 +377,22 @@ static ssize_t qemu_fill_buffer(QEMUFile *f)
>          return 0;
>      }
>  
> -    len = f->ops->get_buffer(f->ioc, f->buf + pending, f->total_transferred,
> -                             IO_BUF_SIZE - pending, &local_error);
> +    do {
> +        len = qio_channel_read(f->ioc,
> +                               (char *)f->buf + pending,
> +                               IO_BUF_SIZE - pending,
> +                               &local_error);
> +        if (len == QIO_CHANNEL_ERR_BLOCK) {
> +            if (qemu_in_coroutine()) {
> +                qio_channel_yield(f->ioc, G_IO_IN);
> +            } else {
> +                qio_channel_wait(f->ioc, G_IO_IN);
> +            }
> +        } else if (len < 0) {
> +            len = EIO;
> +        }
> +    } while (len == QIO_CHANNEL_ERR_BLOCK);
> +

the next code is:
    if (len > 0) {
        f->buf_size += len;
        f->total_transferred += len;      
    } else if (len == 0) {
        qemu_file_set_error_obj(f, -EIO, local_error);
    } else if (len != -EAGAIN) {          
        qemu_file_set_error_obj(f, len, local_error);
    } else {
****    error_free(local_error);          
    }

because of the while loop, we should never actually see
len = QIO_CHANNEL_ERR_BLOCK out of the bottom; so the only
error value we should have is -EIO;  so that error_free is 
not hittable.

Dave

>      if (len > 0) {
>          f->buf_size += len;
>          f->total_transferred += len;
> diff --git a/migration/qemu-file.h b/migration/qemu-file.h
> index 4a3beedb5b..f7ed568894 100644
> --- a/migration/qemu-file.h
> +++ b/migration/qemu-file.h
> @@ -29,14 +29,6 @@
>  #include "exec/cpu-common.h"
>  #include "io/channel.h"
>  
> -/* Read a chunk of data from a file at the given position.  The pos argument
> - * can be ignored if the file is only be used for streaming.  The number of
> - * bytes actually read should be returned.
> - */
> -typedef ssize_t (QEMUFileGetBufferFunc)(void *opaque, uint8_t *buf,
> -                                        int64_t pos, size_t size,
> -                                        Error **errp);
> -
>  /*
>   * This function writes an iovec to file. The handler must write all
>   * of the data or return a negative errno value.
> @@ -77,7 +69,6 @@ typedef size_t (QEMURamSaveFunc)(QEMUFile *f,
>  typedef QEMUFile *(QEMURetPathFunc)(void *opaque);
>  
>  typedef struct QEMUFileOps {
> -    QEMUFileGetBufferFunc *get_buffer;
>      QEMUFileWritevBufferFunc *writev_buffer;
>      QEMURetPathFunc *get_return_path;
>  } QEMUFileOps;
> -- 
> 2.36.1
> 
-- 
Dr. David Alan Gilbert / dgilbert@redhat.com / Manchester, UK