add new system file

hc

2024-02-20 102a0743326a03cd1a1202ceda21e175b7d3575c

 kernel/tools/testing/selftests/memfd/memfd_test.c
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@@ -290,6 +290,40 @@
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 	munmap(p, mfd_def_size);
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 }
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+static void mfd_assert_fork_private_write(int fd)
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+{
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+	int *p;
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+	pid_t pid;
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+
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+	p = mmap(NULL,
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+		 mfd_def_size,
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+		 PROT_READ | PROT_WRITE,
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+		 MAP_PRIVATE,
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+		 fd,
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+		 0);
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+	if (p == MAP_FAILED) {
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+		printf("mmap() failed: %m\n");
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+		abort();
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+	}
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+
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+	p[0] = 22;
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+
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+	pid = fork();
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+	if (pid == 0) {
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+		p[0] = 33;
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+		exit(0);
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+	} else {
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+		waitpid(pid, NULL, 0);
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+
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+		if (p[0] != 22) {
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+			printf("MAP_PRIVATE copy-on-write failed: %m\n");
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+			abort();
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+		}
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+	}
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+
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+	munmap(p, mfd_def_size);
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+}
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+
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 static void mfd_assert_write(int fd)
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 {
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 	ssize_t l;
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@@ -421,6 +455,7 @@
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 			printf("mmap()+mprotect() didn't fail as expected\n");
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 			abort();
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 		}
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+		munmap(p, mfd_def_size);
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 	}
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 	/* verify PUNCH_HOLE fails */
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@@ -760,6 +795,8 @@
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 	mfd_assert_read_shared(fd2);
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 	mfd_fail_write(fd2);
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+	mfd_assert_fork_private_write(fd);
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+
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 	munmap(p, mfd_def_size);
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 	close(fd2);
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 	close(fd);