diff options
| -rw-r--r-- | configure.ac | 2 | ||||
| -rw-r--r-- | src/shared/missing.h | 10 | ||||
| -rw-r--r-- | src/shared/util.c | 48 | ||||
| -rw-r--r-- | src/test/test-util.c | 35 |
4 files changed, 90 insertions, 5 deletions
diff --git a/configure.ac b/configure.ac index 0496f5e3e..3dd40c357 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 5cf179ef0..cdc38b2dd 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 409ccc7ee..64059065d 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 3f1b5487f..3c79f8f4d 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; } |