On Thu, 08 Feb 2007 01:45:10 +0300
Dmitriy Monakhov <[email protected]> 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.
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