Xen devel - Nov 2009 - [PATCH] libxenlight: implement blktap2 support

Hi all,
this patch implements blktap2 support in libxenlight; blktap2 is only
enabled if it is actually supported by the host, otherwise we fall back
to the previous code.
Also for the moment we pretend that disk type file is actually tap:aio.

Signed-off-by: Stefano Stabellini <stefano.stabellini@eu.citrix.com>

---

diff -r d379cfdfd594 tools/libxl/libxl.c
--- a/tools/libxl/libxl.c	Fri Nov 27 16:37:36 2009 +0000
+++ b/tools/libxl/libxl.c	Fri Nov 27 18:48:01 2009 +0000
@@ -904,6 +904,44 @@
 
 
 /******************************************************************************/
+
+static int is_blktap2_supported(void)
+{
+    char buf[1024];
+    FILE *f = fopen("/proc/devices", "r");
+
+    
+    while (fgets(buf, sizeof(buf), f) != NULL) {
+        if (strstr(buf, "blktap2")) {
+            fclose(f);
+            return 1;
+        }
+    }
+    fclose(f);
+    return 0;
+}
+
+static char *get_blktap2_device(struct libxl_ctx *ctx, char *name, char *type)
+{
+    char buf[1024];
+    char *p;
+    int devnum;
+    FILE *f = fopen("/sys/class/blktap2/devices", "r");
+
+    
+    while (!feof(f)) {
+        fscanf(f, "%d %s", &devnum, buf);
+        p = strchr(buf, '':'');
+        p++;
+        if (!strcmp(p, name) && !strncmp(buf, type, 3)) {
+            fclose(f);
+            return libxl_sprintf(ctx, "/dev/xen/blktap-2/tapdev%d",
devnum);
+        }
+    }
+    fclose(f);
+    return NULL;
+}
+
 int libxl_device_disk_add(struct libxl_ctx *ctx, uint32_t domid,
libxl_device_disk *disk)
 {
     flexarray_t *front;
@@ -913,6 +951,7 @@
     unsigned int foffset = 0;
     int devid;
     libxl_device device;
+    int major, minor;
 
     front = flexarray_make(16, 1);
     if (!front)
@@ -931,11 +970,7 @@
     device.kind = DEVICE_VBD;
 
     switch (disk->phystype) {
-        case PHYSTYPE_FILE:
-            return ERROR_NI; /* FIXME */
-            break;
         case PHYSTYPE_PHY: {
-            int major, minor;
 
             device_physdisk_major_minor(disk->physpath, &major,
&minor);
             flexarray_set(back, boffset++, "physical-device");
@@ -947,7 +982,55 @@
             device.backend_kind = DEVICE_VBD;
             break;
         }
+        case PHYSTYPE_FILE:
+            /* let''s pretend is tap:aio for the moment */
+            disk->phystype = PHYSTYPE_AIO;
         case PHYSTYPE_AIO: case PHYSTYPE_QCOW: case PHYSTYPE_QCOW2: case
PHYSTYPE_VHD:
+            if (is_blktap2_supported()) {
+                int rc, c, p[2], tot;
+                char buf[1024], *dev;
+                if ((dev = get_blktap2_device(ctx, disk->physpath,
device_disk_string_of_phystype(disk->phystype))) == NULL) {
+                    if (pipe(p) < 0) {
+                        XL_LOG(ctx, XL_LOG_ERROR, "Failed to create a
pipe");
+                        return -1;
+                    }
+                    rc = fork();
+                    if (rc < 0) {
+                        XL_LOG(ctx, XL_LOG_ERROR, "Failed to fork a new
process");
+                        return -1;
+                    } else if (!rc) { /* child */
+                        int null_r, null_w;
+                        char *args[4];
+                        args[0] = "tapdisk2";
+                        args[1] = "-n";
+                        args[2] = libxl_sprintf(ctx, "%s:%s",
device_disk_string_of_phystype(disk->phystype), disk->physpath);
+                        args[3] = NULL;
+
+                        null_r = open("/dev/null", O_RDONLY);
+                        null_w = open("/dev/null", O_WRONLY);
+                        libxl_exec(ctx, null_r, p[1], null_w,
"/usr/sbin/tapdisk2", args);
+                        XL_LOG(ctx, XL_LOG_ERROR, "Error execing
tapdisk2");
+                    }
+                    close(p[1]);
+                    tot = 0;
+                    while ((c = read(p[0], buf + tot, sizeof(buf) - tot)) >
0)
+                        tot = tot + c;
+                    close(p[0]);
+                    buf[tot - 1] = ''\0'';
+                    dev = buf;
+                }
+                flexarray_set(back, boffset++, "tapdisk-params");
+                flexarray_set(back, boffset++, libxl_sprintf(ctx,
"%s:%s", device_disk_string_of_phystype(disk->phystype),
disk->physpath));
+                flexarray_set(back, boffset++, "params");
+                flexarray_set(back, boffset++, libxl_sprintf(ctx,
"%s", dev));
+                backend_type = "phy";
+                device_physdisk_major_minor(dev, &major, &minor);
+                flexarray_set(back, boffset++, "physical-device");
+                flexarray_set(back, boffset++, libxl_sprintf(ctx,
"%x:%x", major, minor));
+                device.backend_kind = DEVICE_VBD;
+
+                break;
+            }
             flexarray_set(back, boffset++, "params");
             flexarray_set(back, boffset++, libxl_sprintf(ctx,
"%s:%s",
                           device_disk_string_of_phystype(disk->phystype),
disk->physpath));
diff -r d379cfdfd594 tools/libxl/libxl_device.c
--- a/tools/libxl/libxl_device.c	Fri Nov 27 16:37:36 2009 +0000
+++ b/tools/libxl/libxl_device.c	Fri Nov 27 18:48:01 2009 +0000
@@ -119,7 +119,8 @@
         case PHYSTYPE_QCOW: return "tap";
         case PHYSTYPE_VHD: return "tap";
         case PHYSTYPE_AIO: return "tap";
-        case PHYSTYPE_FILE: return "file";
+        /* let''s pretend file is tap:aio */
+        case PHYSTYPE_FILE: return "tap";
         case PHYSTYPE_PHY: return "phy";
         default: return NULL;
     }

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