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Mon, 02 Jul 2018 02:47:38 -0700 (PDT) Subject: Re: [PATCH 3/4] samples/bpf: Check the error of write() and read() To: David Laight , Alexei Starovoitov , Daniel Borkmann Cc: Teng Qin , "netdev@vger.kernel.org" , "linux-kernel@vger.kernel.org" References: <1530522893-8961-1-git-send-email-treeze.taeung@gmail.com> <1530522893-8961-4-git-send-email-treeze.taeung@gmail.com> From: Taeung Song Message-ID: Date: Mon, 2 Jul 2018 18:47:35 +0900 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:52.0) Gecko/20100101 Thunderbird/52.8.0 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hi David Laight, On 07/02/2018 06:25 PM, David Laight wrote: > From: Taeung Song >> Sent: 02 July 2018 10:15 >> test_task_rename() and test_urandom_read() >> can be failed during write() and read(), >> So check the result of them. >> >> Signed-off-by: Taeung Song >> --- >> samples/bpf/test_overhead_user.c | 20 +++++++++++++++----- >> 1 file changed, 15 insertions(+), 5 deletions(-) >> >> diff --git a/samples/bpf/test_overhead_user.c b/samples/bpf/test_overhead_user.c >> index 6caf47a..8a88d9c 100644 >> --- a/samples/bpf/test_overhead_user.c >> +++ b/samples/bpf/test_overhead_user.c >> @@ -6,6 +6,7 @@ >> */ >> #define _GNU_SOURCE >> #include >> +#include >> #include >> #include >> #include >> @@ -44,8 +45,12 @@ static void test_task_rename(int cpu) >> exit(1); >> } >> start_time = time_get_ns(); >> - for (i = 0; i < MAX_CNT; i++) >> - write(fd, buf, sizeof(buf)); >> + for (i = 0; i < MAX_CNT; i++) { >> + if (write(fd, buf, sizeof(buf)) < 0) { >> + printf("task rename failed: %s\n", strerror(errno)); >> + break; > > I'm not sure 'break' generates sensible output. > OK, it seems to be better to off on the above error case instead of break; >> + } >> + } > > What about partial writes?? > Hum.. do you mean just skipping several errors of the above write() ? >> printf("task_rename:%d: %lld events per sec\n", >> cpu, MAX_CNT * 1000000000ll / (time_get_ns() - start_time)); >> close(fd); >> @@ -55,7 +60,7 @@ static void test_urandom_read(int cpu) >> { >> __u64 start_time; >> char buf[4]; >> - int i, fd; >> + int i, fd, err = 0; >> >> fd = open("/dev/urandom", O_RDONLY); >> if (fd < 0) { >> @@ -63,8 +68,13 @@ static void test_urandom_read(int cpu) >> exit(1); >> } >> start_time = time_get_ns(); >> - for (i = 0; i < MAX_CNT; i++) >> - read(fd, buf, sizeof(buf)); >> + for (i = 0; i < MAX_CNT; i++) { >> + err = read(fd, buf, sizeof(buf)); >> + if (err < 0 || err >= sizeof(buf)) { > > Overlong reads indicate that something is seriously awry. > Short reads are valid - but maybe not expected. >> + printf("failed to read from /dev/urandom: %s\n", strerror(errno)); > > > strerror() won't give anything sensible unless err == -1; > You probably want to include the loop count. > >> + break; > > The summary print will be gibberish after break. > Ditto, will change the code to do exit(1); on the err == -1 case. What do you think about it ? Thanks, Taeung >> + } >> + } >> printf("urandom_read:%d: %lld events per sec\n", >> cpu, MAX_CNT * 1000000000ll / (time_get_ns() - start_time)); >> close(fd); >> -- >> 2.7.4 >