[DTrace-devel] [PATCH] bpf, perf: helper functions should return -errno on failure

[Kris Van Hees]

The bpf() and perf_event_open() helper functions were returning -1 on
failure and callers were supposed to check errno.  Since the only valid
values are >= 0, they now return -errno on failure so callers can just
check the return value rather than errno.

Signed-off-by: Kris Van Hees <kris.van.hees at oracle.com>
---
 libdtrace/dt_bpf.c         | 29 ++++++++++++++++++-----------
 libdtrace/dt_prov_rawtp.c  |  4 ++--
 libdtrace/dt_provider_tp.c |  2 +-
 3 files changed, 21 insertions(+), 14 deletions(-)

diff --git a/libdtrace/dt_bpf.c b/libdtrace/dt_bpf.c
index 6c9758a1..8034af48 100644
--- a/libdtrace/dt_bpf.c
+++ b/libdtrace/dt_bpf.c
@@ -31,14 +31,20 @@ int
 perf_event_open(struct perf_event_attr *attr, pid_t pid,
 		    int cpu, int group_fd, unsigned long flags)
 {
-	return syscall(__NR_perf_event_open, attr, pid, cpu, group_fd,
-		       flags | PERF_FLAG_FD_CLOEXEC);
+	int	rc;
+
+	rc = syscall(__NR_perf_event_open, attr, pid, cpu, group_fd,
+		     flags | PERF_FLAG_FD_CLOEXEC);
+	return rc >= 0 ? rc : -errno;
 }
 
 int
 bpf(enum bpf_cmd cmd, union bpf_attr *attr)
 {
-	return syscall(__NR_bpf, cmd, attr, sizeof(union bpf_attr));
+	int	rc;
+
+	rc = syscall(__NR_bpf, cmd, attr, sizeof(union bpf_attr));
+	return rc >= 0 ? rc : -errno;
 }
 
 static int
@@ -92,7 +98,7 @@ dt_bpf_prog_load(enum bpf_prog_type prog_type, const dtrace_difo_t *dp,
 	/* Syscall could return EAGAIN - try at most 5 times. */
 	do {
 		fd = bpf(BPF_PROG_LOAD, &attr);
-	} while (fd < 0 && errno == EAGAIN && ++i < 5);
+	} while (fd == -EAGAIN && ++i < 5);
 
 	return fd;
 }
@@ -143,7 +149,7 @@ dt_bpf_map_create_meta(enum bpf_map_type otype, const char *name,
 
 	ifd =  bpf(BPF_MAP_CREATE, &attr);
 	if (ifd < 0)
-		return -1;
+		return ifd;
 
 	/* Create the map-of-maps. */
 	memset(&attr, 0, sizeof(attr));
@@ -976,7 +982,7 @@ dt_bpf_load_prog(dtrace_hdl_t *dtp, const dt_probe_t *prp,
 {
 	size_t				logsz;
 	char				*log;
-	int				rc, origerrno = 0;
+	int				rc, origerr = 0;
 	const dtrace_probedesc_t	*pdp = prp->desc;
 	char				*p, *q;
 
@@ -996,7 +1002,7 @@ dt_bpf_load_prog(dtrace_hdl_t *dtp, const dt_probe_t *prp,
 		if (rc >= 0)
 			return rc;
 
-		origerrno = errno;
+		origerr = -rc;
 	}
 
 	if (dtp->dt_options[DTRACEOPT_BPFLOGSIZE] != DTRACEOPT_UNSET)
@@ -1008,18 +1014,19 @@ dt_bpf_load_prog(dtrace_hdl_t *dtp, const dt_probe_t *prp,
 	rc = dt_bpf_prog_load(prp->prov->impl->prog_type, dp, 4 | 2 | 1,
 			      log, logsz);
 	if (rc < 0) {
-		char msg[64];
+		char	msg[64];
+		int	err = -rc;
 
 		snprintf(msg, sizeof(msg),
 			 "BPF program load for '%s:%s:%s:%s' failed",
 		         pdp->prv, pdp->mod, pdp->fun, pdp->prb);
-		if (errno == EPERM)
+		if (err == EPERM)
 			return dt_bpf_lockmem_error(dtp, msg);
 		dt_bpf_error(dtp, "%s: %s\n", msg,
-		     strerror(origerrno ? origerrno : errno));
+		     strerror(origerr ? origerr : err));
 
 		/* check whether we have an incomplete BPF log */
-		if (errno == ENOSPC) {
+		if (err == ENOSPC) {
 			fprintf(stderr,
 				"BPF verifier log is incomplete and is not reported.\n"
 				"Set DTrace option 'bpflogsize' to some greater size for more output.\n"
diff --git a/libdtrace/dt_prov_rawtp.c b/libdtrace/dt_prov_rawtp.c
index 1ff0a311..24104dd5 100644
--- a/libdtrace/dt_prov_rawtp.c
+++ b/libdtrace/dt_prov_rawtp.c
@@ -181,11 +181,11 @@ static int probe_info(dtrace_hdl_t *dtp, const dt_probe_t *prp,
 		dif.dtdo_len = 2;
 
 		bpf_fd = dt_bpf_prog_load(dt_rawtp.prog_type, &dif, 0, NULL, 0);
-		if (bpf_fd == -1)
+		if (bpf_fd < 0)
 			continue;
 		rtp_fd = dt_bpf_raw_tracepoint_open(prp->desc->prb, bpf_fd);
 		close(bpf_fd);
-		if (rtp_fd == -1)
+		if (rtp_fd < 0)
 			continue;
 		close(rtp_fd);
 		break;
diff --git a/libdtrace/dt_provider_tp.c b/libdtrace/dt_provider_tp.c
index f3e03323..23766b2a 100644
--- a/libdtrace/dt_provider_tp.c
+++ b/libdtrace/dt_provider_tp.c
@@ -75,7 +75,7 @@ dt_tp_attach(dtrace_hdl_t *dtp, tp_probe_t *tpp, int bpf_fd)
 
 		fd = perf_event_open(&attr, -1, 0, -1, 0);
 		if (fd < 0)
-			return -errno;
+			return fd;
 
 		tpp->event_fd = fd;
 	}
-- 
2.42.0