[Qemu-devel] [PATCH 2/3] monitor: Introduce block_watermark command

[Luiz Capitulino <lcapitulino@redhat.com>]

This command sets a watermark value for a device. The next commit
will add the BLOCK_WATERMARK event, which is emitted when this
value is reached.

Please, note that currently only the 'high' watermark value is
supported.

Signed-off-by: Luiz Capitulino <lcapitulino@redhat.com>
---
 block.c         |    5 +++++
 block.h         |    2 ++
 block_int.h     |    3 +++
 monitor.c       |   46 ++++++++++++++++++++++++++++++++++++++++++++++
 qemu-monitor.hx |   16 ++++++++++++++++
 5 files changed, 72 insertions(+), 0 deletions(-)

diff --git a/block.c b/block.c
index 31d1ba4..260502a 100644
--- a/block.c
+++ b/block.c
@@ -1209,6 +1209,11 @@ void bdrv_flush_all(void)
             bdrv_flush(bs);
 }
 
+void bdrv_set_high_watermark(BlockDriverState *bs, uint64_t offset)
+{
+    bs->high_watermark = offset;
+}
+
 /*
  * Returns true iff the specified sector is present in the disk image. Drivers
  * not implementing the functionality are assumed to not support backing files,
diff --git a/block.h b/block.h
index edf5704..af32436 100644
--- a/block.h
+++ b/block.h
@@ -130,6 +130,8 @@ BlockDriverAIOCB *bdrv_aio_ioctl(BlockDriverState *bs,
 void bdrv_flush(BlockDriverState *bs);
 void bdrv_flush_all(void);
 
+void bdrv_set_high_watermark(BlockDriverState *bs, uint64_t offset);
+
 int bdrv_is_allocated(BlockDriverState *bs, int64_t sector_num, int nb_sectors,
 	int *pnum);
 
diff --git a/block_int.h b/block_int.h
index 50e1a0b..53e087d 100644
--- a/block_int.h
+++ b/block_int.h
@@ -156,6 +156,9 @@ struct BlockDriverState {
 
     void *sync_aiocb;
 
+    /* high watermark for monitor event */
+    uint64_t high_watermark;
+
     /* I/O stats (display with "info blockstats"). */
     uint64_t rd_bytes;
     uint64_t wr_bytes;
diff --git a/monitor.c b/monitor.c
index 672ae47..595bd62 100644
--- a/monitor.c
+++ b/monitor.c
@@ -1041,6 +1041,52 @@ static int do_eject(Monitor *mon, const QDict *qdict, QObject **ret_data)
     return eject_device(mon, bs, force);
 }
 
+static int do_block_set_watermark(Monitor *mon, const QDict *qdict,
+                                  QObject **ret_data)
+{
+    int64_t offset;
+    char format[32];
+    BlockDriverState *bs;
+
+    bs = bdrv_find(qdict_get_str(qdict, "device"));
+    if (!bs) {
+        qemu_error_new(QERR_DEVICE_NOT_FOUND, qdict_get_str(qdict, "device"));
+        return -1;
+    }
+
+    bdrv_get_format(bs, format, sizeof(format));
+
+    if (format[0] == '\0') {
+        qemu_error_new(QERR_DEVICE_NOT_ACTIVE, qdict_get_str(qdict, "device"));
+        return -1;
+    }
+
+    /* we only support qcow2 currently */
+    if (strcmp(format, "qcow2")) {
+        qemu_error_new(QERR_INVALID_BLOCK_FORMAT, format);
+        return -1;
+    }
+
+    if (strcmp(qdict_get_str(qdict, "type"), "high")) {
+        qemu_error_new(QERR_INVALID_PARAMETER, "type");
+        return -1;
+    }
+
+    offset = qdict_get_int(qdict, "offset");
+    if (offset < 0) {
+        qemu_error_new(QERR_INVALID_PARAMETER, "offset");
+        return -1;
+    }
+
+    /* 
+     * XXX: 'offset' is int64_t because the monitor code doesn't
+     * work with uint64_t. Does it matter? If it does, the
+     * monitor has to be fixed.
+     */
+    bdrv_set_high_watermark(bs, offset);
+    return 0;
+}
+
 static int do_block_set_passwd(Monitor *mon, const QDict *qdict,
                                 QObject **ret_data)
 {
diff --git a/qemu-monitor.hx b/qemu-monitor.hx
index 7f9d261..c4b48db 100644
--- a/qemu-monitor.hx
+++ b/qemu-monitor.hx
@@ -1127,6 +1127,22 @@ Set the encrypted device @var{device} password to @var{password}
 ETEXI
 
     {
+        .name       = "block_watermark",
+        .args_type  = "device:B,type:s,offset:l",
+        .params     = "device type offset",
+        .help       = "set block device watermark",
+        .user_print = monitor_user_noop,
+        .mhandler.cmd_new = do_block_set_watermark,
+    },
+
+STEXI
+@item block_watermark @var{device} @var{type} @var{offset}
+@findex block_watermark
+Set the block device @var{device} watermark @var{type} to @var{offset}
+ETEXI
+
+
+    {
         .name       = "qmp_capabilities",
         .args_type  = "",
         .params     = "",
-- 
1.7.0.1