From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from out30-99.freemail.mail.aliyun.com (out30-99.freemail.mail.aliyun.com [115.124.30.99]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 6884A77652; Wed, 24 Jan 2024 12:50:24 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=115.124.30.99 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1706100630; cv=none; b=aa3z79hW6Z5g+WOIoHCbS1mbEgDTpnCGmBoQcUgRJf1LJtyL1ndVSxKCh1ACM5GmEQpp7xP9JOjzELruRMoq/lRB6aOc0iCgoqkXFsZaIFhmTqCG+3HkE3tZlTb40nd5iP2D7H1lBVHfWZk5Up8gLNOqTwfUR6xbc1KlgIA/oNQ= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1706100630; c=relaxed/simple; bh=lRs6RL/zQlcIaeBWW71/aAJ66BXOtnlf6gJLAxRKZck=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=jTGUnOoKVoSRJut6l731PC6+15FRAIcJ9dlWxdE7YqJFFZubG9E9cg+myRZkq3YwHaDKWAUzwSnX3C12BpnSS89ySp4c9v6oGnk6HJMVQo45FY3uz1G9IOY1Bn4xNgQvTICWtcUccT5QMc1afSsO4ktk/UGG7UbBGauG+OLQyIo= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.alibaba.com; spf=pass smtp.mailfrom=linux.alibaba.com; arc=none smtp.client-ip=115.124.30.99 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.alibaba.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=linux.alibaba.com X-Alimail-AntiSpam:AC=PASS;BC=-1|-1;BR=01201311R531e4;CH=green;DM=||false|;DS=||;FP=0|-1|-1|-1|0|-1|-1|-1;HT=ay29a033018045170;MF=jefflexu@linux.alibaba.com;NM=1;PH=DS;RN=4;SR=0;TI=SMTPD_---0W.Gp3dN_1706100621; Received: from 192.168.31.58(mailfrom:jefflexu@linux.alibaba.com fp:SMTPD_---0W.Gp3dN_1706100621) by smtp.aliyun-inc.com; Wed, 24 Jan 2024 20:50:22 +0800 Message-ID: <96abca7f-8bd1-44e8-98be-c60d6d676ec6@linux.alibaba.com> Date: Wed, 24 Jan 2024 20:50:21 +0800 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH] fuse: add support for explicit export disabling Content-Language: en-US To: Miklos Szeredi Cc: linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org, amir73il@gmail.com References: <20240124113042.44300-1-jefflexu@linux.alibaba.com> From: Jingbo Xu In-Reply-To: Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit On 1/24/24 8:16 PM, Miklos Szeredi wrote: > On Wed, 24 Jan 2024 at 12:30, Jingbo Xu wrote: >> >> open_by_handle_at(2) can fail with -ESTALE with a valid handle returned >> by a previous name_to_handle_at(2) for evicted fuse inodes, which is >> especially common when entry_valid_timeout is 0, e.g. when the fuse >> daemon is in "cache=none" mode. >> >> The time sequence is like: >> >> name_to_handle_at(2) # succeed >> evict fuse inode >> open_by_handle_at(2) # fail >> >> The root cause is that, with 0 entry_valid_timeout, the dput() called in >> name_to_handle_at(2) will trigger iput -> evict(), which will send >> FUSE_FORGET to the daemon. The following open_by_handle_at(2) will send >> a new FUSE_LOOKUP request upon inode cache miss since the previous inode >> eviction. Then the fuse daemon may fail the FUSE_LOOKUP request with >> -ENOENT as the cached metadata of the requested inode has already been >> cleaned up during the previous FUSE_FORGET. The returned -ENOENT is >> treated as -ESTALE when open_by_handle_at(2) returns. >> >> This confuses the application somehow, as open_by_handle_at(2) fails >> when the previous name_to_handle_at(2) succeeds. The returned errno is >> also confusing as the requested file is not deleted and already there. >> It is reasonable to fail name_to_handle_at(2) early in this case, after >> which the application can fallback to open(2) to access files. >> >> Since this issue typically appears when entry_valid_timeout is 0 which >> is configured by the fuse daemon, the fuse daemon is the right person to >> explicitly disable the export when required. >> >> Also considering FUSE_EXPORT_SUPPORT actually indicates the support for >> lookups of "." and "..", and there are existing fuse daemons supporting >> export without FUSE_EXPORT_SUPPORT set, for compatibility, we add a new >> INIT flag for such purpose. > > This looks good overall. > >> >> Signed-off-by: Jingbo Xu >> --- >> RFC: https://lore.kernel.org/all/20240123093701.94166-1-jefflexu@linux.alibaba.com/ >> --- >> fs/fuse/inode.c | 11 ++++++++++- >> include/uapi/linux/fuse.h | 2 ++ >> 2 files changed, 12 insertions(+), 1 deletion(-) >> >> diff --git a/fs/fuse/inode.c b/fs/fuse/inode.c >> index 2a6d44f91729..851940c0e930 100644 >> --- a/fs/fuse/inode.c >> +++ b/fs/fuse/inode.c >> @@ -1110,6 +1110,11 @@ static struct dentry *fuse_get_parent(struct dentry *child) >> return parent; >> } >> >> +/* only for fid encoding; no support for file handle */ >> +static const struct export_operations fuse_fid_operations = { > > Nit: I'd call this fuse_no_export_operations (or something else that > emphasizes the fact that this is only for encoding and not for full > export support). OK I will rename it to fuse_no_export_operations. By the way do I need to bump and update the minor version of FUSE protocol? -- Thanks, Jingbo