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

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

[Nicholas A. Bellinger]

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

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

[Christoph Hellwig]

Nick,

can we wait a bit with this series?  With the threadlets currently
pending for inclusion I can get my rewrite of the generic-generic
to not abuse the qemu block layer out of the closet again, which
should simplify a lot of the things you're touching here.

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

[Nicholas A. Bellinger]

On Wed, 2010-11-24 at 17:48 +0100, Christoph Hellwig wrote:
> Nick,
> 
> can we wait a bit with this series?  With the threadlets currently
> pending for inclusion I can get my rewrite of the generic-generic
> to not abuse the qemu block layer out of the closet again, which
> should simplify a lot of the things you're touching here.
> 

Sure, no big rush on this series now that it's been updated to run
against recent v2 QEMU SCSI changes and latest megasas emulation code.
I must have missed your threadlets block rewrite series, but am
interested to see how this can simply things wrt to scsi-generic and
scsi-bsg -> accessing kernel backend devices.

But yeah, the lack of a proper bsg_rq_map_user_iov() handler in
block/bsg.c:bsg_map_hdr() still needs to be addressed in the mainline
kernel, so that SCSIDeviceInfo->alloc_req_iov() generated SCSIRequest
can function properly in patch #5.

--nab

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

[Nicholas A. Bellinger]

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.

It also adds a special case BSG check in find_protocol() using the BSG
major in order to avoid the strchr() for ':' as we expect filenames to
contain /dev/bsg/H:C:T:L.

This path also adds a struct BlockDriverState->fd to save a opened file descriptor
with format_name = 'raw' for use by scsi-bsg.

Signed-off-by: Nicholas A. Bellinger <nab@linux-iscsi.org>
---
 block.c           |   23 ++++++++++++++++++++---
 block.h           |    1 +
 block/raw-posix.c |   17 +++++++++++++++--
 block_int.h       |    5 +++++
 4 files changed, 41 insertions(+), 5 deletions(-)

diff --git a/block.c b/block.c
index 88dbc00..3cd18ec 100644
--- a/block.c
+++ b/block.c
@@ -285,8 +285,12 @@ static BlockDriver *find_protocol(const char *filename)
 {
     BlockDriver *drv1;
     char protocol[128];
-    int len;
+    int len, bsg = 0;
     const char *p;
+#if defined(__linux__)
+    struct stat st;
+#endif
+
 
     /* TODO Drivers without bdrv_file_open must be specified explicitly */
 
@@ -296,7 +300,15 @@ static BlockDriver *find_protocol(const char *filename)
         return bdrv_find_format("file");
 #endif
     p = strchr(filename, ':');
-    if (!p) {
+#if defined(__linux__)
+    if (stat(filename, &st) < 0)
+        return NULL;
+    /* This is not yet defined in include/linux/major.h.. */
+    if (S_ISCHR(st.st_mode) && major(st.st_rdev) == 254)
+        bsg = 1;
+#endif
+
+    if (!p || bsg) {
         drv1 = find_hdev_driver(filename);
         if (!drv1) {
             drv1 = bdrv_find_format("file");
@@ -1209,7 +1221,12 @@ 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 f87d24e..4faeedc 100644
--- a/block.h
+++ b/block.h
@@ -146,6 +146,7 @@ int bdrv_get_translation_hint(BlockDriverState *bs);
 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 1515ca9..d349109 100644
--- a/block/raw-posix.c
+++ b/block/raw-posix.c
@@ -52,6 +52,7 @@
 #include <sys/ioctl.h>
 #include <linux/cdrom.h>
 #include <linux/fd.h>
+#include <linux/major.h>
 #endif
 #if defined (__FreeBSD__) || defined(__FreeBSD_kernel__)
 #include <signal.h>
@@ -843,6 +844,9 @@ static int hdev_probe_device(const char *filename)
 static int hdev_open(BlockDriverState *bs, const char *filename, int flags)
 {
     BDRVRawState *s = bs->opaque;
+#if defined(__linux__)
+    struct stat st;
+#endif
 
 #ifdef CONFIG_COCOA
     if (strstart(filename, "/dev/cdrom", NULL)) {
@@ -873,8 +877,17 @@ static int hdev_open(BlockDriverState *bs, const char *filename, int flags)
 
     s->type = FTYPE_FILE;
 #if defined(__linux__)
-    if (strstart(filename, "/dev/sg", NULL)) {
-        bs->sg = 1;
+    if (stat(filename, &st) < 0) {
+        printf("stat() failed errno: %d\n", errno);
+        return -1;
+    }
+    if (S_ISCHR(st.st_mode)) {
+        if (major(st.st_rdev) == SCSI_GENERIC_MAJOR) {
+            bs->sg = BDS_SCSI_GENERIC;
+        } else if (major(st.st_rdev) == 254) {
+            /* This is not yet defined in include/linux/major.h.. */
+            bs->sg = BDS_BSG;
+        }
     }
 #endif
 
diff --git a/block_int.h b/block_int.h
index 1a7240c..74bcb1a 100644
--- a/block_int.h
+++ b/block_int.h
@@ -40,6 +40,10 @@
 #define BLOCK_OPT_CLUSTER_SIZE  "cluster_size"
 #define BLOCK_OPT_PREALLOC      "preallocation"
 
+#define BDS_NONE            0
+#define BDS_SCSI_GENERIC    1
+#define BDS_BSG             2
+
 typedef struct AIOPool {
     void (*cancel)(BlockDriverAIOCB *acb);
     int aiocb_size;
@@ -141,6 +145,7 @@ 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