From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mout.gmx.net ([212.227.17.20]:58644 "EHLO mout.gmx.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751678AbaIVIog (ORCPT ); Mon, 22 Sep 2014 04:44:36 -0400 From: Marc Dietrich To: Gui Hecheng Cc: linux-btrfs@vger.kernel.org Subject: Re: [PATCH v2] btrfs-progs: fix page align issue for lzo compress in restore Date: Mon, 22 Sep 2014 10:44:28 +0200 Message-ID: <9289647.DTjCLnH1da@fb07-iapwap2> In-Reply-To: <1411374568-8542-1-git-send-email-guihc.fnst@cn.fujitsu.com> References: <1411031454.25255.11.camel@localhost.localdomain> <1411374568-8542-1-git-send-email-guihc.fnst@cn.fujitsu.com> MIME-Version: 1.0 Content-Type: multipart/signed; boundary="nextPart2325624.7oldacUNHT"; micalg="pgp-sha1"; protocol="application/pgp-signature" Sender: linux-btrfs-owner@vger.kernel.org List-ID: --nextPart2325624.7oldacUNHT Content-Transfer-Encoding: 7Bit Content-Type: text/plain; charset="ISO-8859-1" Am Montag, 22. September 2014, 16:29:28 schrieb Gui Hecheng: > When runing restore under lzo compression, "bad compress length" > problems are encountered. > It is because there is a page align problem with the @decompress_lzo, > as follows: > |------| |----|-| |------|...|------| > page ^ page page > | > 3 bytes left > > When lzo compress pages im RAM, lzo will ensure that > the 4 bytes len will be in one page as a whole. > There is a situation that 3 (or less) bytes are left > at the end of a page, and then the 4 bytes len is > stored at the start of the next page. > But the @decompress_lzo doesn't goto the start of > the next page and continue to read the next 4 bytes > which is across two pages, so a random value is fetched > as a "bad compress length". > > So we check page alignment every time before we are going to > fetch the next @len and after the former piece of data is decompressed. > If the current page that we reach has less than 4 bytes left, > then we should fetch the next @len at the start of next page. > > Signed-off-by: Marc Dietrich > Signed-off-by: Gui Hecheng > --- > changelog > v1->v2: adopt alignment check method suggested by Marc > --- > cmds-restore.c | 27 ++++++++++++++++++++++++++- > 1 file changed, 26 insertions(+), 1 deletion(-) > > diff --git a/cmds-restore.c b/cmds-restore.c > index 38a131e..974f45d 100644 > --- a/cmds-restore.c > +++ b/cmds-restore.c > @@ -57,6 +57,9 @@ static int dry_run = 0; > > #define LZO_LEN 4 > #define PAGE_CACHE_SIZE 4096 > +#define PAGE_CACHE_MASK (~(PAGE_CACHE_SIZE - 1)) > +#define PAGE_CACHE_ALIGN(addr) (((addr) + PAGE_CACHE_SIZE - 1) \ > + & PAGE_CACHE_MASK) > #define lzo1x_worst_compress(x) ((x) + ((x) / 16) + 64 + 3) > > static int decompress_zlib(char *inbuf, char *outbuf, u64 compress_len, > @@ -93,6 +96,28 @@ static inline size_t read_compress_length(unsigned char *buf) > return le32_to_cpu(dlen); > } > > +static void align_if_need(size_t *tot_in, size_t *in_len) > +{ > + int tot_in_aligned; > + int bytes_left; > + > + tot_in_aligned = PAGE_CACHE_ALIGN(*tot_in); > + bytes_left = tot_in_aligned - *tot_in; > + > + if (bytes_left >= LZO_LEN) > + return; > + > + /* > + * The LZO_LEN bytes is guaranteed to be > + * in one page as a whole, so if a page > + * has fewer than LZO_LEN bytes left, > + * the LZO_LEN bytes should be fetched > + * at the start of the next page > + */ > + *in_len += tot_in_aligned - *tot_in; in_len += bytes_left; // makes it more readable > + *tot_in = tot_in_aligned; > +} > + > static int decompress_lzo(unsigned char *inbuf, char *outbuf, u64 compress_len, > u64 *decompress_len) > { > @@ -135,8 +160,8 @@ static int decompress_lzo(unsigned char *inbuf, char *outbuf, u64 compress_len, > } > out_len += new_len; > outbuf += new_len; > + align_if_need(&tot_in, &in_len); > inbuf += in_len; > - tot_in += in_len; > } > > *decompress_len = out_len; otherwise, looks good to me. Thanks! Marc --nextPart2325624.7oldacUNHT Content-Type: application/pgp-signature; name="signature.asc" Content-Description: This is a digitally signed message part. Content-Transfer-Encoding: 7Bit -----BEGIN PGP SIGNATURE----- Version: GnuPG v2.0.22 (GNU/Linux) iQEcBAABAgAGBQJUH+FsAAoJEKyeR39HFBto2e4IAKdbtP4rXnYk6MqaB+EkkZMi OnarIefYj3Q2Hzk2o5mkHj4SQHeuTGz6asPOef96qv9YaEvlRFOY5vrBr0V5DMKq z8AZ+spCRTQw7DgbiVFizPTJpHstS28yzBofFMwx2oz+94e15sEIpviyGWqN29yS A6mE6AhyRyrdkuVAEpCbc3JdZ8cdrzv+L9Ea54D+t+d1LrcUBq1PWSvwTcW2Z6cr eB2CLdvaXJf+wG7afsYniSiqUI9c7p+BDLoVkEdHpPv12pmAeoXh31t1IE/AyI4T BkcBNH3WiWHY3Smjy0og4s+gZvCbU5ixFnUMXnbbz62TIkQydAYAcSlXH+YBI44= =ahiQ -----END PGP SIGNATURE----- --nextPart2325624.7oldacUNHT--