ioctl: introduce force xfer length configuration knob

Some controllers can't handle transfers smaller than 4k size. Introduce
an environment variable which allows to force all xfers to 4k.

This is not documented on purpose, as it's rather a crude hack we
don't want to promote.

Signed-off-by: Daniel Wagner <wagi@kernel.org>

Author: igaw

src/nvme/ioctl.c

@@ -320,6 +320,22 @@ int nvme_get_log(struct nvme_get_log_args *args)
 	return nvme_submit_admin_passthru(args->fd, &cmd, args->result);
 }
 
+static bool force_4k;
+
+__attribute__((constructor))
+static void nvme_init_env(void)
+{
+	char *val;
+
+	val = getenv("LIBNVME_FORCE_4K");
+	if (!val)
+		return;
+	if (!strcmp(val, "1") ||
+	    !strcasecmp(val, "true") ||
+	    !strncasecmp(val, "enable", 6))
+		force_4k = true;
+}
+
 #ifdef CONFIG_LIBURING
 enum {
 	IO_URING_NOT_AVAILABLE,
@@ -449,6 +465,9 @@ int nvme_get_log_page(int fd, __u32 xfer_len, struct nvme_get_log_args *args)
 
 	args->fd = fd;
 
+	if (force_4k)
+		xfer_len = NVME_LOG_PAGE_PDU_SIZE;
+
 #ifdef CONFIG_LIBURING
 	int n = 0;
 	struct io_uring ring;
@@ -469,9 +488,13 @@ int nvme_get_log_page(int fd, __u32 xfer_len, struct nvme_get_log_args *args)
 	 * avoids having to check the MDTS value of the controller.
 	 */
 	do {
-		xfer = data_len - offset;
-		if (xfer > xfer_len)
-			xfer  = xfer_len;
+		if (!force_4k) {
+			xfer = data_len - offset;
+			if (xfer > xfer_len)
+				xfer  = xfer_len;
+		} else {
+			xfer = NVME_LOG_PAGE_PDU_SIZE;
+		}
 
 		/*
 		 * Always retain regardless of the RAE parameter until the very