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b2f5de0334
* Test lookup in /proc/self/fd. "map_files" lookup story showed that lookup is not that simple. * Test that all those symlinks open the same file. Check with (st_dev, st_info). * Test that kernel threads do not have anything in their /proc/*/fd/ directory. Now this is where things get interesting. First, kernel threads aren't pinned by /proc/self or equivalent, thus some "atomicity" is required. Second, ->comm can contain whitespace and ')'. No, they are not escaped. Third, the only reliable way to check if process is kernel thread appears to be field #9 in /proc/*/stat. This field is struct task_struct::flags in decimal! Check is done by testing PF_KTHREAD flags like we do in kernel. PF_KTREAD value is a part of userspace ABI !!! Other methods for determining kernel threadness are not reliable: * RSS can be 0 if everything is swapped, even while reading from /proc/self. * ->total_vm CAN BE ZERO if process is finishing munmap(NULL, whole address space); * /proc/*/maps and similar files can be empty because unmapping everything works. Read returning 0 can't distinguish between kernel thread and such suicide process. Link: http://lkml.kernel.org/r/20180505000414.GA15090@avx2 Signed-off-by: Alexey Dobriyan <adobriyan@gmail.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
57 lines
1.6 KiB
C
57 lines
1.6 KiB
C
/*
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* Copyright © 2018 Alexey Dobriyan <adobriyan@gmail.com>
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*
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* Permission to use, copy, modify, and distribute this software for any
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* purpose with or without fee is hereby granted, provided that the above
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* 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 WARRANTIES
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* WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
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* MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
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* ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
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* WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
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* ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
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* OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
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*/
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// Test that open(/proc/*/fd/*) opens the same file.
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#undef NDEBUG
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#include <assert.h>
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#include <stdio.h>
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#include <sys/types.h>
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#include <sys/stat.h>
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#include <fcntl.h>
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#include <unistd.h>
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int main(void)
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{
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int fd0, fd1, fd2;
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struct stat st0, st1, st2;
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char buf[64];
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int rv;
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fd0 = open("/", O_DIRECTORY|O_RDONLY);
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assert(fd0 >= 0);
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snprintf(buf, sizeof(buf), "/proc/self/fd/%u", fd0);
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fd1 = open(buf, O_RDONLY);
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assert(fd1 >= 0);
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snprintf(buf, sizeof(buf), "/proc/thread-self/fd/%u", fd0);
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fd2 = open(buf, O_RDONLY);
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assert(fd2 >= 0);
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rv = fstat(fd0, &st0);
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assert(rv == 0);
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rv = fstat(fd1, &st1);
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assert(rv == 0);
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rv = fstat(fd2, &st2);
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assert(rv == 0);
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assert(st0.st_dev == st1.st_dev);
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assert(st0.st_ino == st1.st_ino);
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assert(st0.st_dev == st2.st_dev);
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assert(st0.st_ino == st2.st_ino);
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return 0;
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}
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