Re: [Qemu-devel] [RFC 01/10] ide: add is_write() macro for semantic consistency

[Paolo Bonzini <pbonzini@redhat.com>]

Il 13/09/2014 06:34, John Snow ha scritto:
> The prepare_buf callback takes an argument named /is_write/,
> however in core.c we are checking to see if this DMA command
> is /is_read/. I am adding a small macro to correct this oversight.
> 
> Impact: Nothing, yet.
> -The prepare_buf callback is only used in ahci and pci, and both
>  versions of this callback name the incoming argument is_write.
> -Both functions ignore this hint currently, anyway.
> 
> This is therefore a simple patch to avoid future mistakes.
> 
> Signed-off-by: John Snow <jsnow@redhat.com>
> ---
>  hw/ide/core.c     | 2 +-
>  hw/ide/internal.h | 2 ++
>  2 files changed, 3 insertions(+), 1 deletion(-)
> 
> diff --git a/hw/ide/core.c b/hw/ide/core.c
> index 191f893..3d682e2 100644
> --- a/hw/ide/core.c
> +++ b/hw/ide/core.c
> @@ -718,7 +718,7 @@ void ide_dma_cb(void *opaque, int ret)
>      n = s->nsector;
>      s->io_buffer_index = 0;
>      s->io_buffer_size = n * 512;
> -    if (s->bus->dma->ops->prepare_buf(s->bus->dma, ide_cmd_is_read(s)) == 0) {
> +    if (s->bus->dma->ops->prepare_buf(s->bus->dma, ide_cmd_is_write(s)) == 0) {
>          /* The PRDs were too short. Reset the Active bit, but don't raise an
>           * interrupt. */
>          s->status = READY_STAT | SEEK_STAT;
> diff --git a/hw/ide/internal.h b/hw/ide/internal.h
> index 5c19f79..72d0147 100644
> --- a/hw/ide/internal.h
> +++ b/hw/ide/internal.h
> @@ -338,6 +338,8 @@ enum ide_dma_cmd {
>  
>  #define ide_cmd_is_read(s) \
>  	((s)->dma_cmd == IDE_DMA_READ)
> +#define ide_cmd_is_write(s) \
> +    ((s)->dma_cmd == IDE_DMA_WRITE)
>  
>  /* NOTE: IDEState represents in fact one drive */
>  struct IDEState {
> 

Actually the code is right (!).

A read command corresponds to a DMA write.  A write or trim will read
data from memory, so it is a DMA read.

See for example how rw_buf is only used from the READ CD command, but
passes 1 for the second argument of prepare_buf.

Paolo