| /* |
| * Copyright (C) 2019 The Android Open Source Project |
| * All rights reserved. |
| * |
| * Redistribution and use in source and binary forms, with or without |
| * modification, are permitted provided that the following conditions |
| * are met: |
| * * Redistributions of source code must retain the above copyright |
| * notice, this list of conditions and the following disclaimer. |
| * * Redistributions in binary form must reproduce the above copyright |
| * notice, this list of conditions and the following disclaimer in |
| * the documentation and/or other materials provided with the |
| * distribution. |
| * |
| * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS |
| * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT |
| * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS |
| * FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE |
| * COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, |
| * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, |
| * BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS |
| * OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED |
| * AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, |
| * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT |
| * OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF |
| * SUCH DAMAGE. |
| */ |
| |
| #include <stdlib.h> |
| |
| #include <errno.h> |
| #include <fcntl.h> |
| #include <string.h> |
| #include <sys/stat.h> |
| |
| #include "private/FdPath.h" |
| #include "private/ScopedFd.h" |
| |
| // This function needs a 4KiB (PATH_MAX) buffer. |
| // The alternative is to heap allocate and then trim, but that's 2x the code. |
| // (Remember that readlink(2) won't tell you the needed size, so the multi-pass |
| // algorithm isn't even an option unless you want to just guess, in which case |
| // you're back needing to trim again.) |
| #pragma GCC diagnostic ignored "-Wframe-larger-than=" |
| |
| char* realpath(const char* path, char* result) { |
| // Weird special case. |
| if (!path) { |
| errno = EINVAL; |
| return nullptr; |
| } |
| |
| // Get an O_PATH fd, and... |
| ScopedFd fd(open(path, O_PATH | O_CLOEXEC)); |
| if (fd.get() == -1) return nullptr; |
| |
| // (...remember the device/inode that we're talking about and...) |
| struct stat sb; |
| if (fstat(fd.get(), &sb) == -1) return nullptr; |
| dev_t st_dev = sb.st_dev; |
| ino_t st_ino = sb.st_ino; |
| |
| // ...ask the kernel to do the hard work for us. |
| FdPath fd_path(fd.get()); |
| char dst[PATH_MAX]; |
| ssize_t l = readlink(fd_path.c_str(), dst, sizeof(dst) - 1); |
| if (l == -1) return nullptr; |
| dst[l] = '\0'; |
| |
| // What if the file was removed in the meantime? readlink(2) will have |
| // returned "/a/b/c (deleted)", and we want to return ENOENT instead. |
| if (stat(dst, &sb) == -1 || st_dev != sb.st_dev || st_ino != sb.st_ino) { |
| errno = ENOENT; |
| return nullptr; |
| } |
| |
| return result ? strcpy(result, dst) : strdup(dst); |
| } |