From: Russell King Subject: Re: Boot failure with ext2 and initrds Date: Wed, 29 Nov 2006 07:40:00 +0000 Message-ID: <20061129074000.GA21352@flint.arm.linux.org.uk> References: <20061114184919.GA16020@skynet.ie> <20061114113120.d4c22b02.akpm@osdl.org> <20061115214534.72e6f2e8.akpm@osdl.org> <455C0B6F.7000201@us.ibm.com> <20061115232228.afaf42f2.akpm@osdl.org> <20061116123448.GA28311@flint.arm.linux.org.uk> <20061125145915.GB13089@flint.arm.linux.org.uk> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Return-path: Received: from caramon.arm.linux.org.uk ([217.147.92.249]:28691 "EHLO caramon.arm.linux.org.uk") by vger.kernel.org with ESMTP id S966206AbWK2IYp (ORCPT ); Wed, 29 Nov 2006 03:24:45 -0500 To: Andrew Morton , Mingming Cao , Hugh Dickins , Mel Gorman , "Martin J. Bligh" , linux-kernel@vger.kernel.org, "linux-ext4@vger.kernel.org" Content-Disposition: inline In-Reply-To: <20061125145915.GB13089@flint.arm.linux.org.uk> Sender: linux-ext4-owner@vger.kernel.org List-Id: linux-ext4.vger.kernel.org Yet another attempt to get a response from Andrew. It is rather important that you DO respond to this. On Sat, Nov 25, 2006 at 02:59:16PM +0000, Russell King wrote: > On Thu, Nov 16, 2006 at 12:34:48PM +0000, Russell King wrote: > > On Wed, Nov 15, 2006 at 11:22:28PM -0800, Andrew Morton wrote: > > > On Wed, 15 Nov 2006 22:55:43 -0800 > > > Mingming Cao wrote: > > > > > > > Hmm, maxblocks, in bitmap_search_next_usable_block(), is the end block > > > > number of the range to search, not the lengh of the range. maxblocks > > > > get passed to ext2_find_next_zero_bit(), where it expecting to take the > > > > _size_ of the range to search instead... > > > > > > > > Something like this: (this is not a patch) > > > > @@ -524,7 +524,7 @@ bitmap_search_next_usable_block(ext2_grp > > > > ext2_grpblk_t next; > > > > > > > > - next = ext2_find_next_zero_bit(bh->b_data, maxblocks, start); > > > > + next = ext2_find_next_zero_bit(bh->b_data, maxblocks-start + 1, start); > > > > if (next >= maxblocks) > > > > return -1; > > > > return next; > > > > } > > > > > > yes, the `size' arg to find_next_zero_bit() represents the number of bits > > > to scan at `offset'. > > > > Are you sure? That's not the way it's implemented in many architectures. > > find_next_*_bit() has always taken "address, maximum offset, starting offset" > > and always has returned "next offset". > > > > Just look at arch/i386/lib/bitops.c: > > > > int find_next_zero_bit(const unsigned long *addr, int size, int offset) > > { > > unsigned long * p = ((unsigned long *) addr) + (offset >> 5); > > int set = 0, bit = offset & 31, res; > > ... > > /* > > * No zero yet, search remaining full bytes for a zero > > */ > > res = find_first_zero_bit (p, size - 32 * (p - (unsigned long *) addr)); > > return (offset + set + res); > > } > > > > So for the case that "offset" is aligned to a "long" boundary, that gives us: > > > > res = find_first_zero_bit(addr + (offset>>5), > > size - 32 * (addr + (offset>>5) - addr)); > > > > or: > > > > res = find_first_zero_bit(addr + (offset>>5), size - (offset & ~31)); > > > > So, size _excludes_ offset. > > > > Now, considering the return value, "res" above will be relative to > > "addr + (offset>>5)". However, we add "offset" on to that, so it's > > relative to addr + (offset bits). > > Andrew, > > Please respond to the above. If what you say is correct then all > architectures need their bitops fixing to fit ext2's requirements. > > -- > Russell King > Linux kernel 2.6 ARM Linux - http://www.arm.linux.org.uk/ > maintainer of: > - > To unsubscribe from this list: send the line "unsubscribe linux-kernel" in > the body of a message to majordomo@vger.kernel.org > More majordomo info at http://vger.kernel.org/majordomo-info.html > Please read the FAQ at http://www.tux.org/lkml/ -- Russell King Linux kernel 2.6 ARM Linux - http://www.arm.linux.org.uk/ maintainer of: