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Date: Wed, 7 Feb 2007 18:11:03 -0800 From: Andrew Morton <akpm@...ux-foundation.org> To: Dmitriy Monakhov <dmonakhov@...nvz.org> Cc: Linux Kernel <linux-kernel@...r.kernel.org> Subject: Re: nobh_truncate_page question On Thu, 08 Feb 2007 01:45:10 +0300 Dmitriy Monakhov <dmonakhov@...nvz.org> wrote: > Could some one please explain me what's happens with nobh_truncate_page? > > int nobh_truncate_page(struct address_space *mapping, loff_t from) > { > ........ > if ((offset & (blocksize - 1)) == 0) > goto out; > > ret = -ENOMEM; > page = grab_cache_page(mapping, index); > if (!page) > goto out; > > to = (offset + blocksize) & ~(blocksize - 1); > ret = a_ops->prepare_write(NULL, page, offset, to); > <<<<< This prepare_write() not balanced by appropriate commit_write() > <<<<< Currently this not is fatal because this function used only > <<<<< by ext2 and jfs witch unbalanced prepare/commit operations > <<<<< not painful. See that comment at the top of nobh_truncate_page()? > if (ret == 0) { > kaddr = kmap_atomic(page, KM_USER0); > memset(kaddr + offset, 0, PAGE_CACHE_SIZE - offset); > flush_dcache_page(page); > kunmap_atomic(kaddr, KM_USER0); > set_page_dirty(page); > } > unlock_page(page); > page_cache_release(page); > out: > return ret; > } > > But we can't just call commit_write after all job done because this result in > i_size increasing till block end. Where are two possible solutions: > a) Call ->commit_write() and then restore i_size to old value. > b) Leave code as it is now, but add warning comment about prepare/commit > balance violation. It just happens that nobh_prepare_write() does all the things which nobh_truncate_page() wants done. If you need to change nobh_prepare_write(), you'll need to change nobh_truncate_page(). Or something. You haven't told us what you're trying to do. - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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