On 03/11/2011 08:05 PM, Samuel Thibault wrote:
Matthew Fioravante, le Fri 11 Mar 2011 17:34:26 -0500, a écrit :
+ /*Make sure we have write permission */
+ if(dev->info.info& VDISK_READONLY || dev->info.mode != O_RDWR) {
O_WRONLY too.
Good catch, actually testing a bitfield with != is a bad idea to begin
with anyway.
+ aiocb.aio_dev = dev;
+ aiocb.aio_buf = _xmalloc(blocksize, dev->info.sector_size);
+ aiocb.aio_nbytes = blocksize;
+ aiocb.aio_offset = blknum * blocksize;
+ aiocb.aio_cb = NULL;
+ aiocb.data = NULL;
+
+ /* read operation */
+ if(!write) {
+ aiocb.aio_cb = NULL;
+ blkfront_read(&aiocb);
+ memcpy(buf,&aiocb.aio_buf[blkoff], bytes);
+ }
Could you perhaps optimize when buf is actually aligned? That would
save a copy.
This can be done but only if in the current iteration of the loop an
entire block is being read. Since aiocb only operates on sectors it'll
read at minimum a whole sector into buf. If buf isnt big enough to hold
the data a secondary buffer with a copy operation will have to be done.
+ /* Write operation */
+ else {
+ /* If we're writing a partial block, we need to read the current
contents first
+ * so we don't overwrite the extra bits with garbage */
+ if(blkoff != 0 || bytes< blocksize) {
+ aiocb.aio_cb = NULL;
Maybe blkfront_aio_cb should do it itself? It looks odd to have to do
it when reusing an aiocb structure.
It could, but then that changes the design of aiocb. Was it supposed to
be a very low level interface for just reading and writing blocks onto
the disk?
Right now you have to set aio_nbytes and aio_offset to a multiple of
sector size. This could be changed to allow variable sizes.
Alternatively 2 new fields could be added to specify which portion
inside a block to operate on.
Can you send a partial block through the xen block frontend and backend
interface? If not we would have to queue up a read and then a write
internally when the user requests a write. Its possible some users may
not want this forced behavior of 2 operations.
Apart from that it looks good.
Samuel
Attachment:
smime.p7s
Description: S/MIME Cryptographic Signature
_______________________________________________
Xen-devel mailing list
Xen-devel@xxxxxxxxxxxxxxxxxxx
http://lists.xensource.com/xen-devel