Automatically check whether to disable cache during prepare

src/disk_tool_utils.cpp

@@ -2,6 +2,7 @@
 // License: VNPL-1.1 (see README.md for details)
 
 #include <sys/wait.h>
+#include <dirent.h>
 
 #include "disk_tool.h"
 #include "rw_blocking.h"
@@ -88,7 +89,9 @@ std::string read_file(std::string file, bool allow_enoent)
     return res;
 }
 
-int check_queue_cache(std::string dev, std::string parent_dev)
+// returns 1 = check error, 0 = write through, -1 = write back
+// (similar to 1 = warning, -1 = error, 0 = success in disable_cache)
+static int check_queue_cache(std::string dev, std::string parent_dev)
 {
     auto r = read_file("/sys/block/"+dev+"/queue/write_cache", true);
     if (r == "")
@@ -98,6 +101,69 @@ int check_queue_cache(std::string dev, std::string parent_dev)
     return trim(r) == "write through" ? 0 : -1;
 }
 
+// returns 1 = warning, -1 = error, 0 = success
+int disable_cache(std::string dev)
+{
+    auto parent_dev = get_parent_device(dev);
+    if (parent_dev == "")
+        return 1;
+    auto scsi_disk = "/sys/block/"+parent_dev+"/device/scsi_disk";
+    DIR *dir = opendir(scsi_disk.c_str());
+    if (!dir)
+    {
+        if (errno == ENOENT)
+        {
+            // Not a SCSI/SATA device, just check /sys/block/.../queue/write_cache
+            return check_queue_cache(dev.substr(5), parent_dev);
+        }
+        else
+        {
+            fprintf(stderr, "Can't read directory %s: %s\n", scsi_disk.c_str(), strerror(errno));
+            return 1;
+        }
+    }
+    else
+    {
+        dirent *de = readdir(dir);
+        while (de && de->d_name[0] == '.' && (de->d_name[1] == 0 || de->d_name[1] == '.' && de->d_name[2] == 0))
+            de = readdir(dir);
+        if (!de)
+        {
+            // Not a SCSI/SATA device, just check /sys/block/.../queue/write_cache
+            closedir(dir);
+            return check_queue_cache(dev.substr(5), parent_dev);
+        }
+        scsi_disk += "/";
+        scsi_disk += de->d_name;
+        if (readdir(dir) != NULL)
+        {
+            // Error, multiple scsi_disk/* entries
+            closedir(dir);
+            fprintf(stderr, "Multiple entries in %s found\n", scsi_disk.c_str());
+            return 1;
+        }
+        closedir(dir);
+        // Check cache_type
+        scsi_disk += "/cache_type";
+        std::string cache_type = read_file(scsi_disk);
+        if (cache_type == "")
+            return 1;
+        if (cache_type == "write back")
+        {
+            int fd = open(scsi_disk.c_str(), O_WRONLY);
+            if (fd < 0 || write_blocking(fd, (void*)"write through", strlen("write through")) != strlen("write through"))
+            {
+                if (fd >= 0)
+                    close(fd);
+                fprintf(stderr, "Can't write to %s: %s\n", scsi_disk.c_str(), strerror(errno));
+                return -1;
+            }
+            close(fd);
+        }
+    }
+    return 0;
+}
+
 std::string get_parent_device(std::string dev)
 {
     if (dev.substr(0, 5) != "/dev/")