From d14389d0f7074e79eb0869baceeef03f4aa7e14f Mon Sep 17 00:00:00 2001
From: Matt Whitlock <sedutil@mattwhitlock.name>
Date: Tue, 1 Dec 2020 19:09:43 -0500
Subject: [PATCH] linux/DtaDevOS.cpp: improve robustness of drive type
 auto-detection

DtaDevOS::init() previously detected the drive type by checking whether
the user-specified device node path starts with "/dev/nvme" or "/dev/s".
This is fragile and breaks mysteriously in cases such as when the user
specifies a relative path to a device node or when the user specifies a
device through a udev-managed symbolic link in /dev/disk/by-id/ et al.

This commit reimplements drive type auto-detection using a more robust
algorithm that stats the specified device node and treats it as a SATA
drive if the device node's major number is one of the SCSI_DISK*_MAJOR
numbers or as an NVMe drive if the device is bound to the "nvme" kernel
driver. (The latter check requires sysfs to be mounted at /sys.)
---
 linux/DtaDevOS.cpp | 72 ++++++++++++++++++++++++++++++++++++++--------
 1 file changed, 60 insertions(+), 12 deletions(-)

diff --git a/linux/DtaDevOS.cpp b/linux/DtaDevOS.cpp
index 5261e736..292cf8d3 100644
--- a/linux/DtaDevOS.cpp
+++ b/linux/DtaDevOS.cpp
@@ -24,12 +24,14 @@ along with sedutil.  If not, see <http://www.gnu.org/licenses/>.
 #include <fnmatch.h>
 #include <fcntl.h>
 #include <sys/ioctl.h>
+#include <sys/sysmacros.h>
 #include <scsi/sg.h>
 #include <stdio.h>
 #include <string.h>
 #include <algorithm>
 #include <unistd.h>
 #include <linux/hdreg.h>
+#include <linux/major.h>
 #include <errno.h>
 #include <vector>
 #include <fstream>
@@ -60,23 +62,69 @@ void DtaDevOS::init(const char * devref)
 	memset(&disk_info, 0, sizeof(OPAL_DiskInfo));
 	dev = devref;
 
-	if (!strncmp(devref, "/dev/nvme", 9))
+	struct stat st;
+	if (stat(devref, &st) < 0)
 	{
-//		DtaDevLinuxNvme *NvmeDrive = new DtaDevLinuxNvme();
-		drive = new DtaDevLinuxNvme();
+		LOG(E) << "DtaDevOS::init ERROR - failed to stat " << devref;
+		isOpen = FALSE;
+		return;
 	}
-	else if (!strncmp(devref, "/dev/s", 6))
+	switch (st.st_mode & S_IFMT)
 	{
-//		DtaDevLinuxSata *SataDrive = new DtaDevLinuxSata();
-		drive = new DtaDevLinuxSata();
+		case S_IFBLK: // block device
+		{
+			switch (major(st.st_rdev))
+			{
+				case SCSI_DISK0_MAJOR:
+				case SCSI_DISK1_MAJOR:
+				case SCSI_DISK2_MAJOR:
+				case SCSI_DISK3_MAJOR:
+				case SCSI_DISK4_MAJOR:
+				case SCSI_DISK5_MAJOR:
+				case SCSI_DISK6_MAJOR:
+				case SCSI_DISK7_MAJOR:
+				case SCSI_DISK8_MAJOR:
+				case SCSI_DISK9_MAJOR:
+				case SCSI_DISK10_MAJOR:
+				case SCSI_DISK11_MAJOR:
+				case SCSI_DISK12_MAJOR:
+				case SCSI_DISK13_MAJOR:
+				case SCSI_DISK14_MAJOR:
+				case SCSI_DISK15_MAJOR:
+				{
+//					DtaDevLinuxSata *SataDrive = new DtaDevLinuxSata();
+					drive = new DtaDevLinuxSata();
+					goto init;
+				}
+			}
+			break;
+		}
+		case S_IFCHR: // character device
+		{
+			char path[PATH_MAX];
+			snprintf(path, sizeof path, "/sys/dev/char/%u:%u/device/driver", major(st.st_rdev), minor(st.st_rdev));
+			ssize_t r;
+			if ((r = readlink(path, path, sizeof path - 1)) < 0)
+			{
+				LOG(E) << "DtaDevOS::init ERROR - failed to readlink " << path;
+				isOpen = FALSE;
+				return;
+			}
+			path[r] = '\0'; // readlink does not append a null terminator
+			if (strcmp(basename(path), "nvme") == 0)
+			{
+//				DtaDevLinuxNvme *NvmeDrive = new DtaDevLinuxNvme();
+				drive = new DtaDevLinuxNvme();
+				goto init;
+			}
+			break;
+		}
 	}
-	else 
-        {
-		LOG(E) << "DtaDevOS::init ERROR - unknown drive type";
-                isOpen = FALSE;
-                return;
-        }
+	LOG(E) << "DtaDevOS::init ERROR - unknown drive type";
+	isOpen = FALSE;
+	return;
 
+init:
 	if (drive->init(devref))
 	{
 		isOpen = TRUE;