22fb267ad6
Use O_PATH like musl to let the kernel do the hard work, rather than the traditional BSD manual scheme. Also add the most obvious missing tests from reading the man page, plus a non-obvious test for deleted files. Bug: http://b/131435126 Test: treehugger Change-Id: Ie8a8986fea55f045952a81afee377ce8288a49d5
78 lines
2.8 KiB
C++
78 lines
2.8 KiB
C++
/*
|
|
* 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);
|
|
}
|