On Wed, 2005-02-09 at 08:37, Stephen C. Tweedie wrote: > Hi, > > On Wed, 2005-02-09 at 16:18, Badari Pulavarty wrote: > > > I am trying to understand journaling code in ext3. > > Can some one enlighten me, why we need journal start > > and stop in ext3_writeback_writepage() ? The block > > allocation is already made in prepare_write(). > > prepare_write()/commit_write() are used for write(2) writes: the data is > dirtied, but not immediately queued for IO (unless you're using O_SYNC). > > writepage is used when you want to write the page's data to disk > *immediately* --- it's used when the VM is swapping out an mmaped file, > or for msync(). > > So when writepage comes in, there's no guarantee that we've had a > previous prepare. You can, for example, use ftruncate() to create a > large hole in a file, and then mmap() it; if you then dirty a page, then > the allocation occurs in the writepage(). So a transaction handle is > necessary. > > --Stephen
Thank you. It make sense now. I was under the impression that writepage() could also be used to flush the data even for write(2) writes. Is it not true ? I was trying to add writepages() interface for ext3. I am wondering if I need to do journaling for that case too. Thanks, Badari - To unsubscribe from this list: send the line "unsubscribe linux-fsdevel" in the body of a message to [EMAIL PROTECTED] More majordomo info at http://vger.kernel.org/majordomo-info.html
