Hello, > May be better call subject something like: "Shortest way to ufs write support", > but current subject give more chances to recieve answer. > > First of all I try explain the current problem: > UFS as other block file systems has notition of "block", > but further to "block" notion it has "fragment" concept. > "fragment" used for preventing waste of space. > Usually fragment==block/8, and if "the rest of file" doesn't occupy > the whole block, it occupy several fragments. If file grows, at some point > "the rest of file" will be occupy 8 fragments. And HERE IS PROBLEM, > we should allocate block and move 8 fragments to it. > > On *BSD/Solaris it is simple: they read analog of buffer_head and > change analog of b_blocknr and that's all. > > The current code of fs/ufs/balloc.c does the same: > ---------------------- > sb_bread > bh->b_blocknr = > mark_buffer_dirty (bh) > brelse (bh) > -------------------------- > I suppose you guess: it doesn't work, > latter when you do sb_getblk(old_blocknr) it give to us the same block > and after that kernel hang up. > > > Hence question: what would be the proper solution in this situation? > Is it possible in current VFS change b_blocknr? I guess it is possible but certainly it's not that easy as just changing b_blocknr. Each buffer head is attached to a page (either to a page of a backing device mapping or to a page belonging to the inode mapping). And if you look at e.g. __find_get_block_slow() you'll see that we look for the buffer using that page. So you definitely need to somehow attach the buffer to the new page at the correct location. Honza -- Jan Kara <jack@xxxxxxx> SuSE CR Labs - 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
