回复: Re: [WIP] [PATCH 04/12] erofs-utils: fuse: adjust larger extent handling

From: "Huang Jianan" <huangjianan@oppo.com>
To: "Gao Xiang" <hsiangkao@aol.com>
Cc: zhangshiming <zhangshiming@oppo.com>,
	linux-erofs <linux-erofs@lists.ozlabs.org>,
	guoweichao <guoweichao@oppo.com>
Subject: 回复: Re: [WIP] [PATCH 04/12] erofs-utils: fuse: adjust larger extent handling
Date: Mon, 19 Oct 2020 12:49:51 +0800	[thread overview]
Message-ID: <2020101912494966296411@oppo.com> (raw)
In-Reply-To: 20201019033251.GA29138@hsiangkao-HP-ZHAN-66-Pro-G1

Hi, Gao Xiang,
Thanks for you answer, I understand now.
In addition, I sent a patch to fix the clerical error here.
It seems that the compilation won't be affected under the default configuration.

Thanks,
Jianan
--------------
Huang Jianan
>Hi Jianan,
>
>On Mon, Oct 19, 2020 at 11:13:42AM +0800, huangjianan@oppo.com wrote:
>> Hi, Gao Xiang锟斤拷
>> ________________________________
>>
>> 锟斤拷锟斤拷锟剿ｏ拷 Gao Xiang<mailto:hsiangkao@aol.com>
>> 锟斤拷锟斤拷时锟戒： 2020-10-17 13:16
>> 锟秸硷拷锟剿ｏ拷 linux-erofs<mailto:linux-erofs@lists.ozlabs.org>
>> 锟斤拷锟酵ｏ拷 Huang Jianan<mailto:huangjianan@oppo.com>; Li Guifu<mailto:bluce.liguifu@huawei.com>; Li Guifu<mailto:bluce.lee@aliyun.com>; Chao Yu<mailto:chao@kernel.org>; Guo Weichao<mailto:guoweichao@oppo.com>; Zhang Shiming<mailto:zhangshiming@oppo.com>; Gao Xiang<mailto:hsiangkao@aol.com>
>> 锟斤拷锟解： [WIP] [PATCH 04/12] erofs-utils: fuse: adjust larger extent handling
>> so more easy to understand.
>>
>> [ let's fold in to the original patch. ]
>> Cc: Huang Jianan <huangjianan@oppo.com>
>> Signed-off-by: Gao Xiang <hsiangkao@aol.com>
>> ---
>> fuse/read.c | 13 +++++++++----
>> 1 file changed, 9 insertions(+), 4 deletions(-)
>>
>> diff --git a/fuse/read.c b/fuse/read.c
>> index 0d0e3b0fa468..dd44adaa1c40 100644
>> --- a/fuse/read.c
>> +++ b/fuse/read.c
>> @@ -112,12 +112,17 @@ size_t erofs_read_data_compression(struct erofs_vnode *vnode, char *buffer,
>> Z_EROFS_COMPRESSION_LZ4 :
>> Z_EROFS_COMPRESSION_SHIFTED;
>> - if (end >= map.m_la + map.m_llen) {
>> - count = map.m_llen;
>> - partial = !(map.m_flags & EROFS_MAP_FULL_MAPPED);
>> - } else {
>> + /*
>> + * trim to the needed size if the returned extent is quite
>> + * larger than requested, and set up partial flag as well.
>> + */
>> + if (end < map.m_la + map.m_llen) {
>> count = end - map.m_la;
>> partial = true;
>> + } else {
>> + ASSERT(end == map.m_la + map_m_llen);
>>
>> I think you mean map.m_llen intesad of map_m_llen.
>> Besides, I don't understand why add ASSERT here.
>> I think this condition will be true if offset+size is exactly the end of a compressed block?
>
>Thanks for your question.
>The idea is that we requested the extent with
>
>       map.m_la = end - 1;
>
>       ret = z_erofs_map_blocks_iter(vnode, &map);
>       if (ret)
>       return ret;
>
>so the extent must include "end - 1", so
>it's impossible that "end > map.m_la + map.m_llen"
>(invalid return).
>
>or the entire extent would be holed extent, anyway,
>that is another extent rather than a data extent.
>
>(BTW, the up-to-date commits is at
>https://git.kernel.org/pub/scm/linux/kernel/git/xiang/erofs-utils.git/log/?h=wip/experimental_fuse
>kindly check out them as well :) )
>
>Thanks,
>Gao Xiang
>
>
>>
>> + count = map.m_llen;
>> + partial = !(map.m_flags & EROFS_MAP_FULL_MAPPED);
>> }
>> if ((off_t)map.m_la < offset) {
>> --
>> 2.24.0
>>
>> Thanks,
>> Jianan
>
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