From mboxrd@z Thu Jan 1 00:00:00 1970 From: Shailesh Kumar Subject: [Block dev] : Qemu block ide_dma_read call routine Date: Tue, 10 Feb 2015 19:51:05 -0800 Message-ID: Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Return-path: List-Unsubscribe: , List-Post: List-Help: List-Subscribe: , Sender: xen-devel-bounces@lists.xen.org Errors-To: xen-devel-bounces@lists.xen.org To: "xen-devel@lists.xen.org" , qemu-devel@nongnu.org List-Id: xen-devel@lists.xenproject.org Hi, I am implementing read equivalent routine in qemu. Can some one help me understand control flow of the qemu read/write implementation. I am using xen-4.2.0 and qemu-1.6.1 My requirement is simple: I have a 1024*1024 buffer already filled with some useful data. Now when windows (my guest OS) does IDE_DMA_READ command to the disk, I want to intercept it and fill data from my private buffer. my intention is to leverage existing dma_read infrastructure and overwrite the read buffer-data at the lowest level of qemu . That way the buffers /vectors "qiov" which are prepared due to cmd IDE_DMA_READ will copy and return data from my data-buffer to guest-OS. I could trace the control from. ide_sector_start_dma -> s->bus->dma->ops->start_dma -> ide_dma_cb ->dma_bdrv_read -> bdrv_aio_readv . ->bdrv_co_aio_rw_vector -> bdrv_co_do_rw "coroutine" -> bdrv_co_do_readv -> drv->bdrv_co_readv (( in my case it is from raw.c raw_co_readv )) -> bdrv_co_readv -> bdrv_co_do_readv ->in bdrv_co_do_rw the bottom half is scheduled bdrv_co_em_bh -->> this will invoke -> ide_dma_cb () which is again the starting point. Looks like there a double-linked list maintained for the coroutine entries and are off loaded to qemu-wait queue during this process. Now I need help to understand where to look for to find the last read/write system call which will get the data out from the disk for guest-OS (windows) . I am seeking suggestions and help for the same. thanks S. Kumar