[Qemu-devel] [PATCH v7 2/4] raw: Recognize zoned backing devices

[Dmitry Fomichev <dmitry.fomichev@wdc.com>]

The purpose of this patch is to recognize a zoned block device (ZBD)
when it is opened as a raw file. The new code initializes the zoned
model propery introduced by the previous commit.

This commit is Linux-specific as it gets the Zoned Block Device Model
value (none/host-managed/host-aware) from sysfs on the host.

In order to avoid code duplication in file-posix.c, a common helper
function is added to read values of sysfs entries under
/sys/block/<dev>/queue. This way, the existing function that reads
the value of "max_segments" entry and the the new function that reads
"zoned" value both share the same helper code.

Signed-off-by: Dmitry Fomichev <dmitry.fomichev@wdc.com>
Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com>
---
 block/file-posix.c | 75 ++++++++++++++++++++++++++++++++++++++--------
 block/io.c         |  5 ++++
 2 files changed, 67 insertions(+), 13 deletions(-)

diff --git a/block/file-posix.c b/block/file-posix.c
index 71f168ee2f..caacb21f07 100644
--- a/block/file-posix.c
+++ b/block/file-posix.c
@@ -1067,15 +1067,13 @@ static int sg_get_max_transfer_length(int fd)
 #endif
 }
 
-static int sg_get_max_segments(int fd)
+static int hdev_read_blk_queue_entry(int fd, const char *key,
+    char *buf, int buf_len)
 {
 #ifdef CONFIG_LINUX
-    char buf[32];
-    const char *end;
     char *sysfspath = NULL;
     int ret;
     int sysfd = -1;
-    long max_segments;
     struct stat st;
 
     if (fstat(fd, &st)) {
@@ -1083,23 +1081,45 @@ static int sg_get_max_segments(int fd)
         goto out;
     }
 
-    sysfspath = g_strdup_printf("/sys/dev/block/%u:%u/queue/max_segments",
-                                major(st.st_rdev), minor(st.st_rdev));
+    sysfspath = g_strdup_printf("/sys/dev/block/%u:%u/queue/%s",
+                                major(st.st_rdev), minor(st.st_rdev), key);
     sysfd = open(sysfspath, O_RDONLY);
     if (sysfd == -1) {
         ret = -errno;
         goto out;
     }
     do {
-        ret = read(sysfd, buf, sizeof(buf) - 1);
+        ret = read(sysfd, buf, buf_len - 1);
     } while (ret == -1 && errno == EINTR);
     if (ret < 0) {
         ret = -errno;
-        goto out;
     } else if (ret == 0) {
         ret = -EIO;
+    }
+out:
+    if (sysfd != -1) {
+        close(sysfd);
+    }
+    g_free(sysfspath);
+    return ret;
+#else
+    return -ENOTSUP;
+#endif
+}
+
+static int sg_get_max_segments(int fd)
+{
+#ifdef CONFIG_LINUX
+    char buf[32];
+    const char *end;
+    int ret;
+    long max_segments;
+
+    ret = hdev_read_blk_queue_entry(fd, "max_segments", buf, sizeof(buf));
+    if (ret < 0) {
         goto out;
     }
+
     buf[ret] = 0;
     /* The file is ended with '\n', pass 'end' to accept that. */
     ret = qemu_strtol(buf, &end, 10, &max_segments);
@@ -1108,22 +1128,45 @@ static int sg_get_max_segments(int fd)
     }
 
 out:
-    if (sysfd != -1) {
-        close(sysfd);
-    }
-    g_free(sysfspath);
     return ret;
 #else
     return -ENOTSUP;
 #endif
 }
 
+static BdrvZonedModel hdev_get_zoned_model(int fd)
+{
+#ifdef CONFIG_LINUX
+    char buf[32];
+    BdrvZonedModel zm = BDRV_ZONED_MODEL_NONE;
+    int ret;
+
+    ret = hdev_read_blk_queue_entry(fd, "zoned", buf, sizeof(buf));
+    if (ret < 0) {
+        goto out;
+    }
+
+    buf[ret - 1] = '\0'; /* replace the newline character with NULL */
+    if (strcmp(buf, "host-managed") == 0) {
+        zm = BDRV_ZONED_MODEL_HM;
+    } else if (strcmp(buf, "host-aware") == 0) {
+        zm = BDRV_ZONED_MODEL_HA;
+    }
+
+out:
+    return zm;
+#else
+    return BDRV_ZONED_MODEL_NONE;
+#endif
+}
+
 static void raw_refresh_limits(BlockDriverState *bs, Error **errp)
 {
     BDRVRawState *s = bs->opaque;
+    int ret;
 
     if (bs->sg) {
-        int ret = sg_get_max_transfer_length(s->fd);
+        ret = sg_get_max_transfer_length(s->fd);
 
         if (ret > 0 && ret <= BDRV_REQUEST_MAX_BYTES) {
             bs->bl.max_transfer = pow2floor(ret);
@@ -1133,6 +1176,12 @@ static void raw_refresh_limits(BlockDriverState *bs, Error **errp)
         if (ret > 0) {
             bs->bl.max_transfer = MIN(bs->bl.max_transfer, ret * getpagesize());
         }
+
+    }
+
+    ret = hdev_get_zoned_model(s->fd);
+    if (ret >= 0) {
+        bs->bl.zoned_model = ret;
     }
 
     raw_probe_alignment(bs, s->fd, errp);
diff --git a/block/io.c b/block/io.c
index 0fa10831ed..147c320061 100644
--- a/block/io.c
+++ b/block/io.c
@@ -157,6 +157,11 @@ void bdrv_refresh_limits(BlockDriverState *bs, Error **errp)
             return;
         }
         bdrv_merge_limits(&bs->bl, &bs->file->bs->bl);
+
+        /* Propagate zoned model */
+        if (!bs->probed) {
+            bs->bl.zoned_model = bs->file->bs->bl.zoned_model;
+        }
     } else {
         bs->bl.min_mem_alignment = 512;
         bs->bl.opt_mem_alignment = getpagesize();
-- 
2.21.0