From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mx0b-001b2d01.pphosted.com ([148.163.158.5]:45316 "EHLO mx0a-001b2d01.pphosted.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S932549AbeBUJz5 (ORCPT ); Wed, 21 Feb 2018 04:55:57 -0500 Received: from pps.filterd (m0098419.ppops.net [127.0.0.1]) by mx0b-001b2d01.pphosted.com (8.16.0.22/8.16.0.22) with SMTP id w1L9sd15017605 for ; Wed, 21 Feb 2018 04:55:56 -0500 Received: from e06smtp10.uk.ibm.com (e06smtp10.uk.ibm.com [195.75.94.106]) by mx0b-001b2d01.pphosted.com with ESMTP id 2g93fuy4sv-1 (version=TLSv1.2 cipher=AES256-SHA bits=256 verify=NOT) for ; Wed, 21 Feb 2018 04:55:56 -0500 Received: from localhost by e06smtp10.uk.ibm.com with IBM ESMTP SMTP Gateway: Authorized Use Only! Violators will be prosecuted for from ; Wed, 21 Feb 2018 09:55:51 -0000 From: Chandan Rajendra To: Eric Biggers Cc: linux-ext4@vger.kernel.org, linux-fsdevel@vger.kernel.org, linux-fscrypt@vger.kernel.org, tytso@mit.edu Subject: Re: [RFC PATCH V2 05/11] ext4: Decrypt all boundary blocks when doing buffered write Date: Wed, 21 Feb 2018 15:27:18 +0530 In-Reply-To: <20180221010155.GC252219@gmail.com> References: <20180212094347.22071-1-chandan@linux.vnet.ibm.com> <20180212094347.22071-6-chandan@linux.vnet.ibm.com> <20180221010155.GC252219@gmail.com> MIME-Version: 1.0 Content-Transfer-Encoding: 7Bit Content-Type: text/plain; charset="us-ascii" Message-Id: <11341004.sBrkMnv4Fk@localhost.localdomain> Sender: linux-fsdevel-owner@vger.kernel.org List-ID: On Wednesday, February 21, 2018 6:31:55 AM IST Eric Biggers wrote: > Hi Chandan, > > On Mon, Feb 12, 2018 at 03:13:41PM +0530, Chandan Rajendra wrote: > > With block size < page size, ext4_block_write_begin() can have up to two > > blocks to decrypt. Hence this commit invokes fscrypt_decrypt_block() for > > each of those blocks. > > > > Signed-off-by: Chandan Rajendra > > --- > > fs/ext4/inode.c | 33 +++++++++++++++++++++++---------- > > 1 file changed, 23 insertions(+), 10 deletions(-) > > > > diff --git a/fs/ext4/inode.c b/fs/ext4/inode.c > > index 69a4fd6..180dd2d 100644 > > --- a/fs/ext4/inode.c > > +++ b/fs/ext4/inode.c > > @@ -1158,12 +1158,13 @@ static int ext4_block_write_begin(struct page *page, loff_t pos, unsigned len, > > unsigned to = from + len; > > struct inode *inode = page->mapping->host; > > unsigned block_start, block_end; > > - sector_t block; > > + sector_t block, page_blk_nr; > > int err = 0; > > unsigned blocksize = inode->i_sb->s_blocksize; > > unsigned bbits; > > struct buffer_head *bh, *head, *wait[2], **wait_bh = wait; > > bool decrypt = false; > > + int i; > > > > BUG_ON(!PageLocked(page)); > > BUG_ON(from > PAGE_SIZE); > > @@ -1224,18 +1225,30 @@ static int ext4_block_write_begin(struct page *page, loff_t pos, unsigned len, > > /* > > * If we issued read requests, let them complete. > > */ > > - while (wait_bh > wait) { > > - wait_on_buffer(*--wait_bh); > > - if (!buffer_uptodate(*wait_bh)) > > + for (i = 0; &wait[i] < wait_bh; i++) { > > + wait_on_buffer(wait[i]); > > + if (!buffer_uptodate(wait[i])) > > err = -EIO; > > } > > [...] > > > + for (i = 0; &wait[i] < wait_bh; i++) { > > + int err2; > > + > > + --wait_bh; > > + block = page_blk_nr + (bh_offset(wait[i]) >> bbits); > > + err2 = fscrypt_decrypt_block(page->mapping->host, page, > > + wait[i]->b_size, > > + bh_offset(wait[i]), > > + block); > > + if (err2) { > > + clear_buffer_uptodate(wait[i]); > > + err = err2; > > + } > > + } > > These are very confusing ways to iterate through an array, especially the second > loop which is actually going in reverse order (why?). Why not just use a > variable like 'nr_wait' for the number of valid buffer_head's like I had > suggested? Then you can just do 'for (i = 0; i < nr_wait; i++)'. > Sorry, the "--wait_bh;" part was a remanent from the "RFC PATCH V1". Without that statement, we loop in increasing order of elements in wait[] array. I will use the 'nr_wait' counter approach and post the next version of the patchset. I misunderstood your advice to mean that the code should use similar looping order in both loops. -- chandan