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