[Block dev] : Qemu block ide_dma_read call routine

[Shailesh Kumar <tsaileshkumar@gmail.com>]

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