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-rw-r--r--configure.ac2
-rw-r--r--src/shared/missing.h10
-rw-r--r--src/shared/util.c48
-rw-r--r--src/test/test-util.c35
4 files changed, 90 insertions, 5 deletions
diff --git a/configure.ac b/configure.ac
index 0496f5e3ed..3dd40c3578 100644
--- a/configure.ac
+++ b/configure.ac
@@ -310,7 +310,7 @@ LIBS="$save_LIBS"
AC_CHECK_FUNCS([memfd_create])
AC_CHECK_FUNCS([__secure_getenv secure_getenv])
-AC_CHECK_DECLS([gettid, pivot_root, name_to_handle_at, setns, getrandom, renameat2, LO_FLAGS_PARTSCAN],
+AC_CHECK_DECLS([gettid, pivot_root, name_to_handle_at, setns, getrandom, renameat2, kcmp, LO_FLAGS_PARTSCAN],
[], [], [[
#include <sys/types.h>
#include <unistd.h>
diff --git a/src/shared/missing.h b/src/shared/missing.h
index 5cf179ef00..cdc38b2dd8 100644
--- a/src/shared/missing.h
+++ b/src/shared/missing.h
@@ -711,3 +711,13 @@ static inline int renameat2(int oldfd, const char *oldname, int newfd, const cha
#ifndef RENAME_NOREPLACE
#define RENAME_NOREPLACE (1 << 0)
#endif
+
+#if !HAVE_DECL_KCMP
+static inline int kcmp(pid_t pid1, pid_t pid2, int type, unsigned long idx1, unsigned long idx2) {
+ return syscall(__NR_kcmp, pid1, pid2, type, idx1, idx2);
+}
+#endif
+
+#ifndef KCMP_FILE
+#define KCMP_FILE 0
+#endif
diff --git a/src/shared/util.c b/src/shared/util.c
index 409ccc7eed..64059065d8 100644
--- a/src/shared/util.c
+++ b/src/shared/util.c
@@ -7678,13 +7678,35 @@ int fd_setcrtime(int fd, usec_t usec) {
int same_fd(int a, int b) {
struct stat sta, stb;
+ pid_t pid;
+ int r, fa, fb;
assert(a >= 0);
assert(b >= 0);
+ /* Compares two file descriptors. Note that semantics are
+ * quite different depending on whether we have kcmp() or we
+ * don't. If we have kcmp() this will only return true for
+ * dup()ed file descriptors, but not otherwise. If we don't
+ * have kcmp() this will also return true for two fds of the same
+ * file, created by separate open() calls. Since we use this
+ * call mostly for filtering out duplicates in the fd store
+ * this difference hopefully doesn't matter too much. */
+
if (a == b)
return true;
+ /* Try to use kcmp() if we have it. */
+ pid = getpid();
+ r = kcmp(pid, pid, KCMP_FILE, a, b);
+ if (r == 0)
+ return true;
+ if (r > 0)
+ return false;
+ if (errno != ENOSYS)
+ return -errno;
+
+ /* We don't have kcmp(), use fstat() instead. */
if (fstat(a, &sta) < 0)
return -errno;
@@ -7694,9 +7716,27 @@ int same_fd(int a, int b) {
if ((sta.st_mode & S_IFMT) != (stb.st_mode & S_IFMT))
return false;
- if (S_ISREG(sta.st_mode) || S_ISDIR(sta.st_mode) || S_ISFIFO(sta.st_mode) || S_ISSOCK(sta.st_mode) || S_ISLNK(sta.st_mode))
- return (sta.st_dev == stb.st_dev) && (sta.st_ino == stb.st_ino);
+ /* We consider all device fds different, since two device fds
+ * might refer to quite different device contexts even though
+ * they share the same inode and backing dev_t. */
- /* We consider all device fds different... */
- return false;
+ if (S_ISCHR(sta.st_mode) || S_ISBLK(sta.st_mode))
+ return false;
+
+ if (sta.st_dev != stb.st_dev || sta.st_ino != stb.st_ino)
+ return false;
+
+ /* The fds refer to the same inode on disk, let's also check
+ * if they have the same fd flags. This is useful to
+ * distuingish the read and write side of a pipe created with
+ * pipe(). */
+ fa = fcntl(a, F_GETFL);
+ if (fa < 0)
+ return -errno;
+
+ fb = fcntl(b, F_GETFL);
+ if (fb < 0)
+ return -errno;
+
+ return fa == fb;
}
diff --git a/src/test/test-util.c b/src/test/test-util.c
index 3f1b5487f0..3c79f8f4d9 100644
--- a/src/test/test-util.c
+++ b/src/test/test-util.c
@@ -1381,6 +1381,40 @@ static void test_raw_clone(void) {
}
}
+static void test_same_fd(void) {
+ _cleanup_close_pair_ int p[2] = { -1, -1 };
+ _cleanup_close_ int a = -1, b = -1, c = -1;
+
+ assert_se(pipe2(p, O_CLOEXEC) >= 0);
+ assert_se((a = dup(p[0])) >= 0);
+ assert_se((b = open("/dev/null", O_RDONLY|O_CLOEXEC)) >= 0);
+ assert_se((c = dup(a)) >= 0);
+
+ assert_se(same_fd(p[0], p[0]) > 0);
+ assert_se(same_fd(p[1], p[1]) > 0);
+ assert_se(same_fd(a, a) > 0);
+ assert_se(same_fd(b, b) > 0);
+
+ assert_se(same_fd(a, p[0]) > 0);
+ assert_se(same_fd(p[0], a) > 0);
+ assert_se(same_fd(c, p[0]) > 0);
+ assert_se(same_fd(p[0], c) > 0);
+ assert_se(same_fd(a, c) > 0);
+ assert_se(same_fd(c, a) > 0);
+
+ assert_se(same_fd(p[0], p[1]) == 0);
+ assert_se(same_fd(p[1], p[0]) == 0);
+ assert_se(same_fd(p[0], b) == 0);
+ assert_se(same_fd(b, p[0]) == 0);
+ assert_se(same_fd(p[1], a) == 0);
+ assert_se(same_fd(a, p[1]) == 0);
+ assert_se(same_fd(p[1], b) == 0);
+ assert_se(same_fd(b, p[1]) == 0);
+
+ assert_se(same_fd(a, b) == 0);
+ assert_se(same_fd(b, a) == 0);
+}
+
int main(int argc, char *argv[]) {
log_parse_environment();
log_open();
@@ -1455,6 +1489,7 @@ int main(int argc, char *argv[]) {
test_unquote_many_words();
test_parse_proc_cmdline();
test_raw_clone();
+ test_same_fd();
return 0;
}