From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-wr0-f194.google.com (mail-wr0-f194.google.com [209.85.128.194]) by dpdk.org (Postfix) with ESMTP id DAE8D1AFEC for ; Thu, 7 Jun 2018 09:39:14 +0200 (CEST) Received: by mail-wr0-f194.google.com with SMTP id d2-v6so8889226wrm.10 for ; Thu, 07 Jun 2018 00:39:14 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=6wind-com.20150623.gappssmtp.com; s=20150623; h=date:from:to:cc:subject:message-id:references:mime-version :content-disposition:content-transfer-encoding:in-reply-to :user-agent; bh=HCOUZppk88Ruw2jG9O6pHCc7UOm+d1/uB6fH/AHgHlg=; b=YOTDzh8QdopxA1C4RlxhKO1PX85XHFyvcTHnEE11HhdbmVRq5Js/NEZrFSYNUaD6oU uLAJQtqDRrdSfllGqInDnN1ZQmy2DFlfhuPFQDpybPY6kY6H2fgYf4BWZqgekGH3towo AFYTR1OVWfo7QvY5ruaa+Sa80I/Xs0/cVdjEUVDGxoGBIWqB4oe7SPpyayoPpx3aOdpT ClqaYhs3yQ4vsH5tW9blP75hoGymco8icJoOVPMBVnnv7lgRb9bFoYNRECLD/R6wORHh MH3kb8KfzMOAmBn3DMFCX77e3TQP0qjXO9ccw7xHDFQ8e9GevNCYwll2GWGYSeD1oe0G rPgQ== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:date:from:to:cc:subject:message-id:references :mime-version:content-disposition:content-transfer-encoding :in-reply-to:user-agent; bh=HCOUZppk88Ruw2jG9O6pHCc7UOm+d1/uB6fH/AHgHlg=; b=iJbtImut9vBxP2iO7BjhkRjL0IWckspwnf6T6w2nWBPOziVUbqHcJV/Js5wOI6WkqW y2oBCMEdOHuVwiT2utINKgZT8LL6gsSxSK72Uesmo0gpV8GI6l9v0KWxCmAf+bwfL5cF HzVNnWojaJht0uzt60udmefDal5hPHss0YpeuP3d+9oHkwxCuRts5YG5xMhNfNN0lwie 9UgszDj0iPVYDR3XNQsr+Zg9jva6ip76o4acNsrXHBU4E5WQ01Vef+kHYb1wI6HQR63B 7Bv4/IC5Vh3wQc2DapOBnugpz+QhQmnG3is3oypVtHIAqHyju3oDJV3cBPpcAkBDE8BL xA0A== X-Gm-Message-State: APt69E1n2sXRBDrd+W7Eto2VrYyeigMuWMVMlVdhNl6wxnRW0HG/4k5J +x99DqoIGLMUovHjscNvXZ1/w30LQQ== X-Google-Smtp-Source: ADUXVKLfo0LPnaFFaKM6sQqxGcccFRRbGZQaChtXmqA5I2QRZuyaQBwOrkLwJW3JtkBAm6GgXs8jTQ== X-Received: by 2002:adf:c32b:: with SMTP id n40-v6mr700693wrf.91.1528357154497; Thu, 07 Jun 2018 00:39:14 -0700 (PDT) Received: from laranjeiro-vm.dev.6wind.com (host.78.145.23.62.rev.coltfrance.com. [62.23.145.78]) by smtp.gmail.com with ESMTPSA id y5-v6sm9422775wrp.51.2018.06.07.00.39.13 (version=TLS1_2 cipher=ECDHE-RSA-CHACHA20-POLY1305 bits=256/256); Thu, 07 Jun 2018 00:39:13 -0700 (PDT) Date: Thu, 7 Jun 2018 09:39:44 +0200 From: =?iso-8859-1?Q?N=E9lio?= Laranjeiro To: Yongseok Koh Cc: Adrien Mazarguil , "dev@dpdk.org" , Shahaf Shuler , dpdk stable , "Xueming(Steven) Li" Message-ID: <20180607073944.zewdysx6ddrdygoz@laranjeiro-vm.dev.6wind.com> References: <20180604173731.29125-1-yskoh@mellanox.com> <20180605065246.mw7xnk24cfwxy4an@laranjeiro-vm.dev.6wind.com> <84C956B6-28EE-4F82-97AE-5E9C371DD115@mellanox.com> <20180606065501.hhrfrti47nr5xigo@laranjeiro-vm.dev.6wind.com> <20180606183926.GA1446@yongseok-MBP.local> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <20180606183926.GA1446@yongseok-MBP.local> User-Agent: NeoMutt/20170113 (1.7.2) Subject: Re: [dpdk-dev] [PATCH] net/mlx5: fix error number handling X-BeenThere: dev@dpdk.org X-Mailman-Version: 2.1.15 Precedence: list List-Id: DPDK patches and discussions List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Thu, 07 Jun 2018 07:39:15 -0000 On Wed, Jun 06, 2018 at 11:39:27AM -0700, Yongseok Koh wrote: > On Wed, Jun 06, 2018 at 08:55:01AM +0200, Nélio Laranjeiro wrote: > > On Tue, Jun 05, 2018 at 09:36:32PM +0000, Yongseok Koh wrote: > > > > On Jun 4, 2018, at 11:52 PM, Nélio Laranjeiro wrote: > > > > > > > > On Mon, Jun 04, 2018 at 10:37:31AM -0700, Yongseok Koh wrote: > > > >> rte_errno should be saved only if error has occurred because rte_errno > > > >> could have garbage value. > > > >> > > > >> Fixes: a6d83b6a9209 ("net/mlx5: standardize on negative errno values") > > > >> Cc: stable@dpdk.org > > > >> > > > >> Signed-off-by: Yongseok Koh > > > >> --- > > > >> drivers/net/mlx5/mlx5_flow.c | 3 ++- > > > >> 1 file changed, 2 insertions(+), 1 deletion(-) > > > >> > > > >> diff --git a/drivers/net/mlx5/mlx5_flow.c b/drivers/net/mlx5/mlx5_flow.c > > > >> index 994be05be..eaffe7495 100644 > > > >> --- a/drivers/net/mlx5/mlx5_flow.c > > > >> +++ b/drivers/net/mlx5/mlx5_flow.c > > > >> @@ -3561,7 +3561,8 @@ mlx5_fdir_filter_delete(struct rte_eth_dev *dev, > > > >> /* The flow does not match. */ > > > >> continue; > > > >> } > > > >> - ret = rte_errno; /* Save rte_errno before cleanup. */ > > > >> + if (ret) > > > >> + ret = rte_errno; /* Save rte_errno before cleanup. */ > > > >> if (flow) > > > >> mlx5_flow_list_destroy(dev, &priv->flows, flow); > > > >> exit: > > > >> -- > > > >> 2.11.0 > > > > > > > > This patch is not enough, the returned value being -rte_errno if no > > > > error is detected by the function it cannot set rte_errno nor return it. > > > > > > We may need to refactor this kind of code (saving and restoring rte_errno). I > > > still don't understand why we should preserve rte_errno like this. > > > > > > Even if this function returns success, there's no obligation to preserve > > > rte_errno in the function. Once it is called, the ownership of rte_errno belongs > > > to this function. > > > > > > I can't find how we define this per-lcore variable but, from > > > the man page of errno, > > > > > > The header file defines the integer variable errno, which > > > is set by system calls and some library functions in the event of an > > > error to indicate what went wrong. Its value is significant only when > > > the return value of the call indicated an error (i.e., -1 from most > > > system calls; -1 or NULL from most library functions); > > > a function that succeeds is allowed to change errno. > > > > > > So, I still think an API can change rte_errno even if it succeeds, no need to > > > preserve it. If needed, the caller has to save it. > > > > Functions in this PMD are defined as is: > > > > * @return > > * 0 on success, a negative errno value otherwise and rte_errno is set. > > > > Which means rte_errno is only modified in case of error. > > > > This fix does not respect the documentation of the function or any other > > function of the PMD which can return errors. > > That's logically a wrong interpretation. According to the description, if > returning error, rte_errno is set but the opposite isn't always true. Even if > rte_errno is set, it doesn't mean there's an error. So the description coincides > with that of errno. If you want to enforce preserving rte_errno in case of > success, you should amend the documentation. > > > rte_errno is only set if an error is encountered and contains only the error > > code of the first error sub-sequent ones are considered consequences of the > > first one and thus not preserved. > > > > Not preserving the rte_errno in roll backs is equivalent to not setting > > it at all as a function called by the rollback may also set it, example: > > > > { > > void * a; > > > > foo_do(); > > a = malloc(10); > > if (!a) { > > rte_errno = ENOMEM; > > foo_undo(); > > This example is weird. You can simply set rte_errno after foo_undo() in this > case. > > > return -rte_errno; > > } > > } > > > > If foo_undo() also encounter an error it will modify the rte_errno which > > may have a value different from ENOMEM, for the callee won't be informed > > the error is due to a memory issue and thus cannot make counter parts. > > In such situation the rte_errno must be preserved to keep the ENOMEM > > error code. > > I knew it. That's why rte_errno is saved before calling another API which may > change the rte_errno inside. But, we are talking about a case where an API > returns success. If caller is supposed to save rte_errno (when it's needed), why > does callee have to put some effort to preserve it even in case of success? If > rte_errno must be preserved even in case of success, we have to make a big > change to preserve rte_errno for cases where a void function is called (or cases > where we don't check its return value of non-void function). > > > This is also the main reason almost all system function only update > > errno when no error is encountered. > > 'Almost' doesn't mean 'all", does it? It is true that such functions must update > errno when it returns error but it doesn't care about the value when it returns > success. Like the man page I attached above, the errno is significant only when > it returns an error. And "a function that succeeds is allowed to change errno." It is "almost" because a system function touching the errno when the function succeed it not common. But as the man page says it is not impossible. > So, the decision point is whether we want to preserve rte_errno in case of > success? My opinion is no. I did not understood it was only a concern about the success of the function, even it is better to avoid as most as possible a useless store, in this specific case, as errno (rte_errno) has a garbage value, I fully agree with you. Regards, -- Nélio Laranjeiro 6WIND