On 01/23/2012 04:27 PM, Jeff Moyer wrote: > Niels de Vos <ndevos@xxxxxxxxxx> writes: > >> Executing an fsync() on a file-descriptor of a partition flushes the >> caches for that partition by calling blkdev_issue_flush(). However, it >> seems that reading data through the parent device will still return the >> old cached data. > > What problem, exactly, are you trying to fix? Could you please post a > reproducer? The problem that was noticed is the following: 1) create two or more partitions on a device - use fdisk to create /dev/sdb1 and /dev/sdb2 2) format and mount one of the partition - mkfs -t ext3 /dev/sdb1 3) read through the main device to have something in the cache - read /dev/sdb with dd or use something like "parted /dev/sdb print" 4) now write something to /dev/sdb2, format the partition for example - mkfs -t ext3 /dev/sdb2 5) read the blocks where sdb2 starts, through /dev/sdb - use dd or do again a "parted /dev/sdb print" Without this patch, calling "blockdev --flushbufs" or dropping the caches, the result in 5) is the same as in 3). Reading the same area through /dev/sdb2 shows the inconsistancy between the two caches. With this patch, or one of the workarounds, the data read through /dev/sdb and /dev/sdb2 is the same. I hope this explains is clear enough, if not, please let me know. Thanks, Niels -- To unsubscribe from this list: send the line "unsubscribe linux-fsdevel" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
