[Qemu-devel] [PATCH 1/5] block: Add top level BSG support

["Nicholas A. Bellinger" <nab@linux-iscsi.org>]

From: Nicholas Bellinger <nab@linux-iscsi.org>

This patch adds top level BSG support to QEMU-KVM block and adds the
BDS_* prefixed defines for SG_IO and BSG.

It adds the BDS_SCSI_GENERIC and BDS_BSG assignments in block/raw-posix.c:hdev_open()
using S_ISCHR() and major(st.st_rdev) in order to determine when we are dealing with
scsi-generic or scsi-bsg backstores.

Signed-off-by: Nicholas A. Bellinger <nab@linux-iscsi.org>
---
 block.c           |    7 +++++-
 block.h           |    1 +
 block/raw-posix.c |   65 +++++++++++++++++++++++++++++++++++++++++++++++++---
 block_int.h       |    6 +++++
 4 files changed, 74 insertions(+), 5 deletions(-)

diff --git a/block.c b/block.c
index 6b505fb..8faf25d 100644
--- a/block.c
+++ b/block.c
@@ -1340,7 +1340,12 @@ int bdrv_is_read_only(BlockDriverState *bs)
 
 int bdrv_is_sg(BlockDriverState *bs)
 {
-    return bs->sg;
+    return bs->sg == BDS_SCSI_GENERIC;
+}
+
+int bdrv_is_bsg(BlockDriverState *bs)
+{
+    return bs->sg == BDS_BSG;
 }
 
 int bdrv_enable_write_cache(BlockDriverState *bs)
diff --git a/block.h b/block.h
index 78ecfac..5869c8c 100644
--- a/block.h
+++ b/block.h
@@ -174,6 +174,7 @@ void bdrv_set_removable(BlockDriverState *bs, int removable);
 int bdrv_is_removable(BlockDriverState *bs);
 int bdrv_is_read_only(BlockDriverState *bs);
 int bdrv_is_sg(BlockDriverState *bs);
+int bdrv_is_bsg(BlockDriverState *bs);
 int bdrv_enable_write_cache(BlockDriverState *bs);
 int bdrv_is_inserted(BlockDriverState *bs);
 int bdrv_media_changed(BlockDriverState *bs);
diff --git a/block/raw-posix.c b/block/raw-posix.c
index bf89717..2802c97 100644
--- a/block/raw-posix.c
+++ b/block/raw-posix.c
@@ -53,6 +53,7 @@
 #include <sys/param.h>
 #include <linux/cdrom.h>
 #include <linux/fd.h>
+#include <linux/major.h>
 #endif
 #if defined (__FreeBSD__) || defined(__FreeBSD_kernel__)
 #include <signal.h>
@@ -885,13 +886,69 @@ static int hdev_open(BlockDriverState *bs, const char *filename, int flags)
     s->type = FTYPE_FILE;
 #if defined(__linux__)
     {
-        char resolved_path[ MAXPATHLEN ], *temp;
+        struct stat st, st2;
+        FILE *file;
+        char major[8], dev[64], path[128], *p, *buf;
+        int ch, i;
 
-        temp = realpath(filename, resolved_path);
-        if (temp && strstart(temp, "/dev/sg", NULL)) {
-            bs->sg = 1;
+        if (stat(filename, &st) < 0) {
+            printf("stat() failed errno: %d\n", errno);
+            return -1;
+        }
+
+        if (major(st.st_rdev) == SCSI_GENERIC_MAJOR) {
+            bs->sg = BDS_SCSI_GENERIC;
+            goto out;
+        }
+
+        memset(major, 0, 8);
+        memset(dev, 0, 64);
+        memset(path, 0, 128);
+
+        buf = strdup(filename);
+        if (!buf)
+            goto out;
+        /*
+         * Locate the device name from the path, we are interested
+         * in the last strsep() token..
+         */
+        while ((p = strsep(&buf, "/")))
+             snprintf(dev, 64, "%s", p);
+        /*
+         * Check to sure the sysfs entry exists before calling open
+         */
+        snprintf(path, 128, "/sys/class/bsg/%s/dev", dev);
+        if (stat(path, &st2) < 0) {
+            free(buf);
+            goto out;
+        }
+
+        file = fopen(path, "r");
+        if (!file) {
+            printf("fopen() failed for BSG sysfs path: %s\n", path);
+            free(buf);
+            goto out;
+        }
+        ch = fgetc(file);
+        for (i = 0; i < 7; i++) {
+            if (ch == ':') {
+                major[i] = '\0';
+                break;
+            }
+            major[i] = ch;
+            ch = fgetc(file);
         }
+        fclose(file);
+        /*
+         * If the major returned by /sys/class/bsg/$H:C:T:L/dev matches
+         * stat(), then we signal BDS_BSG usage.
+         */
+        if (major(st.st_rdev) == atoi(major))
+             bs->sg = BDS_BSG;
+
+        free(buf);
     }
+out:
 #endif
 
     return raw_open_common(bs, filename, flags, 0);
diff --git a/block_int.h b/block_int.h
index 3c3adb5..8fdc816 100644
--- a/block_int.h
+++ b/block_int.h
@@ -40,6 +40,11 @@
 #define BLOCK_OPT_CLUSTER_SIZE  "cluster_size"
 #define BLOCK_OPT_PREALLOC      "preallocation"
 
+/* Used for BlockDriverState->sg */
+#define BDS_NONE            0
+#define BDS_SCSI_GENERIC    1
+#define BDS_BSG             2
+
 typedef struct AIOPool {
     void (*cancel)(BlockDriverAIOCB *acb);
     int aiocb_size;
@@ -150,6 +155,7 @@ struct BlockDriverState {
     int encrypted; /* if true, the media is encrypted */
     int valid_key; /* if true, a valid encryption key has been set */
     int sg;        /* if true, the device is a /dev/sg* */
+    int fd;        /* Used for BSG file descriptor */
     /* event callback when inserting/removing */
     void (*change_cb)(void *opaque);
     void *change_opaque;
-- 
1.5.6.5