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https://github.com/jart/cosmopolitan.git
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761c6ad615
This change ensures that if a file descriptor for an open disk file gets shared by multiple processes within a process tree, then lseek() changes will be visible across processes, and read() / write() are synchronized. Note this only applies to Windows, because UNIX kernels already do this.
107 lines
2.4 KiB
C
107 lines
2.4 KiB
C
// Copyright 2024 Justine Alexandra Roberts Tunney
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//
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// Permission to use, copy, modify, and/or distribute this software for
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// any purpose with or without fee is hereby granted, provided that the
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// above copyright notice and this permission notice appear in all copies.
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//
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// THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL
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// WARRANTIES WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED
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// WARRANTIES OF MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE
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// AUTHOR BE LIABLE FOR ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL
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// DAMAGES OR ANY DAMAGES WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR
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// PROFITS, WHETHER IN AN ACTION OF CONTRACT, NEGLIGENCE OR OTHER
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// TORTIOUS ACTION, ARISING OUT OF OR IN CONNECTION WITH THE USE OR
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// PERFORMANCE OF THIS SOFTWARE.
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#include <stdatomic.h>
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#include <stdlib.h>
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#include <sys/mman.h>
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#include <unistd.h>
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// test that file offset is shared across multiple processes
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atomic_int *phase;
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int main() {
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if ((phase = mmap(0, sizeof(atomic_int), PROT_READ | PROT_WRITE,
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MAP_SHARED | MAP_ANONYMOUS, -1, 0)) == MAP_FAILED)
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return 1;
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int fd;
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char path[] = "/tmp/fd_test.XXXXXX";
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if ((fd = mkstemp(path)) == -1)
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return 2;
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if (lseek(fd, 0, SEEK_CUR) != 0)
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return 22;
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if (write(fd, "0", 1) != 1)
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return 3;
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if (lseek(fd, 0, SEEK_CUR) != 1)
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return 33;
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int pid;
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if ((pid = fork()) == -1)
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return 4;
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if (!pid) {
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if (write(fd, "1", 1) != 1)
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_Exit(100);
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if (lseek(fd, 0, SEEK_CUR) != 2)
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_Exit(101);
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*phase = 1;
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for (;;)
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if (*phase == 2)
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break;
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if (write(fd, "3", 1) != 1)
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_Exit(102);
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if (lseek(fd, 0, SEEK_CUR) != 4)
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_Exit(103);
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*phase = 3;
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_Exit(0);
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}
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for (;;)
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if (*phase == 1)
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break;
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if (write(fd, "2", 1) != 1)
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return 5;
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if (lseek(fd, 0, SEEK_CUR) != 3)
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return 55;
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*phase = 2;
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for (;;)
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if (*phase == 3)
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break;
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if (write(fd, "4", 1) != 1)
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return 6;
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if (lseek(fd, 0, SEEK_CUR) != 5)
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return 66;
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int ws;
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if (wait(&ws) == -1)
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return 7;
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if (!WIFEXITED(ws))
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return 8;
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if (WEXITSTATUS(ws))
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return WEXITSTATUS(ws);
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char buf[16] = {0};
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if (pread(fd, buf, 15, 0) != 5)
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return 12;
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if (lseek(fd, 0, SEEK_CUR) != 5)
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return 77;
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if (close(fd))
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return 13;
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if (unlink(path))
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return 14;
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if (strcmp(buf, "01234"))
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return 15;
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}
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