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Tue, 27 Oct 2020 05:59:49 -0700 (PDT) Received: from [192.168.1.4] ([177.194.48.209]) by smtp.googlemail.com with ESMTPSA id 29sm601169qks.28.2020.10.27.05.59.48 for (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Tue, 27 Oct 2020 05:59:48 -0700 (PDT) Subject: Re: [PATCH 4/4] stdlib: Remove lstat usage from realpath [BZ #24970] From: Adhemerval Zanella To: libc-alpha@sourceware.org References: <20200910151915.1982465-1-adhemerval.zanella@linaro.org> <20200910151915.1982465-4-adhemerval.zanella@linaro.org> Autocrypt: addr=adhemerval.zanella@linaro.org; prefer-encrypt=mutual; keydata= mQINBFcVGkoBEADiQU2x/cBBmAVf5C2d1xgz6zCnlCefbqaflUBw4hB/bEME40QsrVzWZ5Nq 8kxkEczZzAOKkkvv4pRVLlLn/zDtFXhlcvQRJ3yFMGqzBjofucOrmdYkOGo0uCaoJKPT186L NWp53SACXguFJpnw4ODI64ziInzXQs/rUJqrFoVIlrPDmNv/LUv1OVPKz20ETjgfpg8MNwG6 iMizMefCl+RbtXbIEZ3TE/IaDT/jcOirjv96lBKrc/pAL0h/O71Kwbbp43fimW80GhjiaN2y WGByepnkAVP7FyNarhdDpJhoDmUk9yfwNuIuESaCQtfd3vgKKuo6grcKZ8bHy7IXX1XJj2X/ BgRVhVgMHAnDPFIkXtP+SiarkUaLjGzCz7XkUn4XAGDskBNfbizFqYUQCaL2FdbW3DeZqNIa nSzKAZK7Dm9+0VVSRZXP89w71Y7JUV56xL/PlOE+YKKFdEw+gQjQi0e+DZILAtFjJLoCrkEX w4LluMhYX/X8XP6/C3xW0yOZhvHYyn72sV4yJ1uyc/qz3OY32CRy+bwPzAMAkhdwcORA3JPb kPTlimhQqVgvca8m+MQ/JFZ6D+K7QPyvEv7bQ7M+IzFmTkOCwCJ3xqOD6GjX3aphk8Sr0dq3 4Awlf5xFDAG8dn8Uuutb7naGBd/fEv6t8dfkNyzj6yvc4jpVxwARAQABtElBZGhlbWVydmFs IFphbmVsbGEgTmV0dG8gKExpbmFybyBWUE4gS2V5KSA8YWRoZW1lcnZhbC56YW5lbGxhQGxp bmFyby5vcmc+iQI3BBMBCAAhBQJXFRpKAhsDBQsJCAcDBRUKCQgLBRYCAwEAAh4BAheAAAoJ EKqx7BSnlIjv0e8P/1YOYoNkvJ+AJcNUaM5a2SA9oAKjSJ/M/EN4Id5Ow41ZJS4lUA0apSXW NjQg3VeVc2RiHab2LIB4MxdJhaWTuzfLkYnBeoy4u6njYcaoSwf3g9dSsvsl3mhtuzm6aXFH /Qsauav77enJh99tI4T+58rp0EuLhDsQbnBic/ukYNv7sQV8dy9KxA54yLnYUFqH6pfH8Lly sTVAMyi5Fg5O5/hVV+Z0Kpr+ZocC1YFJkTsNLAW5EIYSP9ftniqaVsim7MNmodv/zqK0IyDB GLLH1kjhvb5+6ySGlWbMTomt/or/uvMgulz0bRS+LUyOmlfXDdT+t38VPKBBVwFMarNuREU2 69M3a3jdTfScboDd2ck1u7l+QbaGoHZQ8ZNUrzgObltjohiIsazqkgYDQzXIMrD9H19E+8fw kCNUlXxjEgH/Kg8DlpoYJXSJCX0fjMWfXywL6ZXc2xyG/hbl5hvsLNmqDpLpc1CfKcA0BkK+ k8R57fr91mTCppSwwKJYO9T+8J+o4ho/CJnK/jBy1pWKMYJPvvrpdBCWq3MfzVpXYdahRKHI ypk8m4QlRlbOXWJ3TDd/SKNfSSrWgwRSg7XCjSlR7PNzNFXTULLB34sZhjrN6Q8NQZsZnMNs TX8nlGOVrKolnQPjKCLwCyu8PhllU8OwbSMKskcD1PSkG6h3r0AquQINBFcVGkoBEACgAdbR Ck+fsfOVwT8zowMiL3l9a2DP3Eeak23ifdZG+8Avb/SImpv0UMSbRfnw/N81IWwlbjkjbGTu oT37iZHLRwYUFmA8fZX0wNDNKQUUTjN6XalJmvhdz9l71H3WnE0wneEM5ahu5V1L1utUWTyh VUwzX1lwJeV3vyrNgI1kYOaeuNVvq7npNR6t6XxEpqPsNc6O77I12XELic2+36YibyqlTJIQ V1SZEbIy26AbC2zH9WqaKyGyQnr/IPbTJ2Lv0dM3RaXoVf+CeK7gB2B+w1hZummD21c1Laua +VIMPCUQ+EM8W9EtX+0iJXxI+wsztLT6vltQcm+5Q7tY+HFUucizJkAOAz98YFucwKefbkTp eKvCfCwiM1bGatZEFFKIlvJ2QNMQNiUrqJBlW9nZp/k7pbG3oStOjvawD9ZbP9e0fnlWJIsj 6c7pX354Yi7kxIk/6gREidHLLqEb/otuwt1aoMPg97iUgDV5mlNef77lWE8vxmlY0FBWIXuZ yv0XYxf1WF6dRizwFFbxvUZzIJp3spAao7jLsQj1DbD2s5+S1BW09A0mI/1DjB6EhNN+4bDB SJCOv/ReK3tFJXuj/HbyDrOdoMt8aIFbe7YFLEExHpSk+HgN05Lg5TyTro8oW7TSMTk+8a5M kzaH4UGXTTBDP/g5cfL3RFPl79ubXwARAQABiQIfBBgBCAAJBQJXFRpKAhsMAAoJEKqx7BSn lIjvI/8P/jg0jl4Tbvg3B5kT6PxJOXHYu9OoyaHLcay6Cd+ZrOd1VQQCbOcgLFbf4Yr+rE9l mYsY67AUgq2QKmVVbn9pjvGsEaz8UmfDnz5epUhDxC6yRRvY4hreMXZhPZ1pbMa6A0a/WOSt AgFj5V6Z4dXGTM/lNManr0HjXxbUYv2WfbNt3/07Db9T+GZkpUotC6iknsTA4rJi6u2ls0W9 1UIvW4o01vb4nZRCj4rni0g6eWoQCGoVDk/xFfy7ZliR5B+3Z3EWRJcQskip/QAHjbLa3pml xAZ484fVxgeESOoaeC9TiBIp0NfH8akWOI0HpBCiBD5xaCTvR7ujUWMvhsX2n881r/hNlR9g fcE6q00qHSPAEgGr1bnFv74/1vbKtjeXLCcRKk3Ulw0bY1OoDxWQr86T2fZGJ/HIZuVVBf3+ gaYJF92GXFynHnea14nFFuFgOni0Mi1zDxYH/8yGGBXvo14KWd8JOW0NJPaCDFJkdS5hu0VY 7vJwKcyHJGxsCLU+Et0mryX8qZwqibJIzu7kUJQdQDljbRPDFd/xmGUFCQiQAncSilYOcxNU EMVCXPAQTteqkvA+gNqSaK1NM9tY0eQ4iJpo+aoX8HAcn4sZzt2pfUB9vQMTBJ2d4+m/qO6+ cFTAceXmIoFsN8+gFN3i8Is3u12u8xGudcBPvpoy4OoG Message-ID: <227ca5fc-0741-ac67-8417-cb4c19c5f217@linaro.org> Date: Tue, 27 Oct 2020 09:59:46 -0300 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.10.0 MIME-Version: 1.0 In-Reply-To: <20200910151915.1982465-4-adhemerval.zanella@linaro.org> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit X-Spam-Status: No, score=-15.3 required=5.0 tests=BAYES_00, DKIM_SIGNED, DKIM_VALID, DKIM_VALID_AU, DKIM_VALID_EF, GIT_PATCH_0, NICE_REPLY_A, RCVD_IN_DNSWL_NONE, SPF_HELO_NONE, SPF_PASS, TXREP autolearn=ham autolearn_force=no version=3.4.2 X-Spam-Checker-Version: SpamAssassin 3.4.2 (2018-09-13) on server2.sourceware.org X-BeenThere: libc-alpha@sourceware.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Libc-alpha mailing list List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Tue, 27 Oct 2020 12:59:52 -0000 Ping. On 10/09/2020 12:19, Adhemerval Zanella wrote: > The readlink already tells whether the file is a symlink, so there is > no need to call lstat to check it. However for '..' it requires an > extra readlink check if the previous component can be really accessed, > otherwise the next iteration will check a possible valid path and end > early. It should performance-wise acceptable and a gain over lstat, > afaik symlink should not update any inode information. > > Checked on x86_64-linux-gnu and i686-linux-gnu. > --- > stdlib/canonicalize.c | 52 ++++++++++++++++++++++--------------------- > 1 file changed, 27 insertions(+), 25 deletions(-) > > diff --git a/stdlib/canonicalize.c b/stdlib/canonicalize.c > index 44a25a9a59..952f4dca41 100644 > --- a/stdlib/canonicalize.c > +++ b/stdlib/canonicalize.c > @@ -55,6 +55,7 @@ __realpath (const char *name, char *resolved) > const char *start, *end, *rpath_limit; > const size_t path_max = PATH_MAX; > int num_links = 0; > + char buf[PATH_MAX]; > char extra_buf[PATH_MAX]; > > if (name == NULL) > @@ -104,12 +105,6 @@ __realpath (const char *name, char *resolved) > > for (end = start; *start; start = end) > { > -#ifdef _LIBC > - struct stat64 st; > -#else > - struct stat st; > -#endif > - > /* Skip sequence of multiple path-separators. */ > while (*start == '/') > ++start; > @@ -118,12 +113,25 @@ __realpath (const char *name, char *resolved) > for (end = start; *end && *end != '/'; ++end) > /* Nothing. */; > > - if (end - start == 0) > - break; > - else if (end - start == 1 && start[0] == '.') > + if (end - start == 1 && start[0] == '.') > /* nothing */; > else if (end - start == 2 && start[0] == '.' && start[1] == '.') > { > + ssize_t n; > + > + if (dest[-1] != '/') > + *dest++ = '/'; > + *dest = '\0'; > + > + n = __readlink (rpath, buf, path_max - 1); > + if (n == -1) > + { > + if (errno == ENOTDIR && dest[-1] == '/') > + dest[-1] = '\0'; > + if (errno != EINVAL) > + goto error; > + } > + > /* Back up to previous component, ignore if at root already. */ > if (dest > rpath + 1) > for (--dest; dest > rpath && dest[-1] != '/'; --dest) > @@ -132,6 +140,7 @@ __realpath (const char *name, char *resolved) > else > { > size_t new_size; > + ssize_t n; > > if (dest[-1] != '/') > *dest++ = '/'; > @@ -166,25 +175,23 @@ __realpath (const char *name, char *resolved) > dest = __mempcpy (dest, start, end - start); > *dest = '\0'; > > - if (__lxstat64 (_STAT_VER, rpath, &st) < 0) > - goto error; > - > - if (S_ISLNK (st.st_mode)) > + n = __readlink (rpath, buf, path_max - 1); > + if (n < 0) > + { > + if (errno == ENOTDIR && dest[-1] == '/') > + dest[-1] = '\0'; > + if (errno != EINVAL) > + goto error; > + } > + else > { > - char buf[PATH_MAX]; > size_t len; > - ssize_t n; > > if (++num_links > __eloop_threshold ()) > { > __set_errno (ELOOP); > goto error; } > > - n = __readlink (rpath, buf, path_max - 1); > - if (n < 0) > - goto error; > - buf[n] = '\0'; > - > len = strlen (end); > /* Check that n + len + 1 doesn't overflow and is <= path_max. */ > if (n >= SIZE_MAX - len || n + len >= path_max) > @@ -211,11 +218,6 @@ __realpath (const char *name, char *resolved) > continue; > } > } > - else if (!S_ISDIR (st.st_mode) && *end != '\0') > - { > - __set_errno (ENOTDIR); > - goto error; > - } > } > } > if (dest > rpath + 1 && dest[-1] == '/') >