src/register: improve RLIMIT_NOFILE increase

Only do it if we run into EMFILE, seems like the prudent thing to do,
avoiding any getrlimit checking if the operation succeeds. And more
importantly, add to the rlim_cur, don't just set it to what we need.

Signed-off-by: Jens Axboe <axboe@kernel.dk>

src/register.c

@@ -119,16 +119,14 @@ int io_uring_register_files_update(struct io_uring *ring, unsigned off,
 	return ret;
 }
 
-static int bump_rlimit_nofile(unsigned nr)
+static int increase_rlimit_nofile(unsigned nr)
 {
 	struct rlimit rlim;
 
 	if (getrlimit(RLIMIT_NOFILE, &rlim) < 0)
 		return -errno;
 	if (rlim.rlim_cur < nr) {
-		if (nr > rlim.rlim_max)
-			return -EMFILE;
-		rlim.rlim_cur = nr;
+		rlim.rlim_cur += nr;
 		setrlimit(RLIMIT_NOFILE, &rlim);
 	}
 
@@ -144,32 +142,45 @@ int io_uring_register_files_tags(struct io_uring *ring,
 		.data = (unsigned long)files,
 		.tags = (unsigned long)tags,
 	};
-	int ret;
-
-	ret = bump_rlimit_nofile(nr);
-	if (ret)
-		return ret;
+	int ret, did_increase = 0;
+
+	do {
+		ret = __sys_io_uring_register(ring->ring_fd,
+					      IORING_REGISTER_FILES2, &reg,
+					      sizeof(reg));
+		if (ret >= 0)
+			break;
+		if (errno == EMFILE && !did_increase) {
+			did_increase = 1;
+			increase_rlimit_nofile(nr);
+			continue;
+		}
+		break;
+	} while (1);
 
-	ret = __sys_io_uring_register(ring->ring_fd, IORING_REGISTER_FILES2,
-				      &reg, sizeof(reg));
 	return ret < 0 ? -errno : ret;
 }
 
 int io_uring_register_files(struct io_uring *ring, const int *files,
 			      unsigned nr_files)
 {
-	int ret;
-
-	ret = bump_rlimit_nofile(nr_files);
-	if (ret)
-		return ret;
+	int ret, did_increase = 0;
+
+	do {
+		ret = __sys_io_uring_register(ring->ring_fd,
+					      IORING_REGISTER_FILES, files,
+					      nr_files);
+		if (ret >= 0)
+			break;
+		if (errno == EMFILE && !did_increase) {
+			did_increase = 1;
+			increase_rlimit_nofile(nr_files);
+			continue;
+		}
+		break;
+	} while (1);
 
-	ret = __sys_io_uring_register(ring->ring_fd, IORING_REGISTER_FILES,
-					files, nr_files);
-	if (ret < 0)
-		return -errno;
-
-	return 0;
+	return ret < 0 ? -errno : ret;
 }
 
 int io_uring_unregister_files(struct io_uring *ring)