Hi all,
I'm porting a NAND flash driver to linux 2.6.27. The NAND driver is
based on NFTL, not kernel MTD subsystem. That is, it will report to
kernel as a standard linux block device, so it can be used as a normal
hard disk.
The NAND driver uses an internal write-back cache to improve R/W
performance. And it provides a function to force flush the cache. But
as it requires in our project that, after a successful umount to ext3
file system, even if the system encountered an un-expected power-down,
user data stored in NAND still need to be correct after system reboot.
Now I have add some code in the driver like this:
-----------------------------------------------------------------------------------
static void SBD_prepare_flush(struct request_queue *q, struct request *rq)
{
rq->cmd_type = REQ_TYPE_LINUX_BLOCK;
/* rq->timeout = 5 * HZ; */
rq->cmd[0] = REQ_LB_OP_FLUSH;
}
...
blk_queue_ordered(dev->queue, QUEUE_ORDERED_DRAIN_FLUSH, SBD_prepare_flush);
...
while (((req = elv_next_request(q)) != NULL)) {
if (req->cmd_type == REQ_TYPE_LINUX_BLOCK &&
req->cmd[0] == REQ_LB_OP_FLUSH) {
printk(KERN_ERR "Will flush cache\n");
/* Cache flush */
if (GLOB_FTL_Flush_Cache()) {
printk(KERN_ERR "Failed to flush FTL cache\n");
end_request(req, 0);
} else
end_request(req, 1);
continue;
}
if (!blk_fs_request(req)) {
nand_dbg_print(NAND_DBG_WARN,
"Spectra: Skip non-fs request\n");
end_request(req, 0);
continue;
}
sectors_xferred = SBD_xfer_request(req);
success = (sectors_xferred < 0) ? 0 : 1;
__blk_end_request(req, success ? 0 : -EIO,
sectors_xferred << 9);
}
...
----------------------------------------------------------------------------------------------------
But this code doesn't work. I mounted ext3 file system, copy a file,
then wait for serveral minutes, then umount file system and power
down. And during the whole process, the flush function is never
called. I tested this in a initrd (busybox) environment.
Does I need to do something else to enable barrier support in linux kernel?
Or, the driver should flush cache once the 'umount' or 'sync' command
is executed? But I don't know how to do it.
It'll be very appreciated if you could give me some suggests or
comments about this. Thank you very much.
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