[Qemu-devel] [PATCH 2/4] block: add block topology options

[Christoph Hellwig <hch@lst.de>]

Add three new suboptions for the drive option to export block topology
information to the guest.  This is needed to get optimal I/O alignment
for RAID arrays or SSDs.

The options are:

 - physical_block_size to specify the physical block size of the device,
   this is going to increase from 512 bytes to 4096 kilobytes for many
   modern storage devices
 - min_io_size to specify the minimal I/O size without performance impact,
   this is typically set to the RAID chunk size for arrays.
 - opt_io_size to specify the optimal sustained I/O size, this is
   typically the RAID stripe width for arrays.

I decided to not auto-probe these values from blkid which might easily
be possible as I don't know how to deal with these issues on migration.

Note that we specificly only set the physical_block_size, and not the
logial one which is the unit all I/O is described in.  The reason for
that is that IDE does not support increasing the logical block size and
at last for now I want to stick to one meachnisms in queue and allow
for easy switching of transports for a given backing image which would
not be possible if scsi and virtio use real 4k sectors, while ide only
uses the physical block exponent.

Signed-off-by: Christoph Hellwig <hch@lst.de>

Index: qemu/block.c
===================================================================
--- qemu.orig/block.c	2010-01-29 11:07:50.083004364 +0100
+++ qemu/block.c	2010-01-29 11:08:32.940004255 +0100
@@ -1028,6 +1028,51 @@ int bdrv_enable_write_cache(BlockDriverS
     return bs->enable_write_cache;
 }
 
+unsigned int bdrv_get_physical_block_size(BlockDriverState *bs)
+{
+    return bs->physical_block_size;
+}
+
+unsigned int bdrv_get_physical_block_exp(BlockDriverState *bs)
+{
+    unsigned int exp = 0, size;
+
+    for (size = bs->physical_block_size; size > 512; size >>= 1) {
+        exp++;
+    }
+
+    return exp;
+}
+
+void bdrv_set_physical_block_size(BlockDriverState *bs,
+        unsigned int physical_block_size)
+{
+    bs->physical_block_size = physical_block_size;
+}
+
+
+unsigned int bdrv_get_min_io_size(BlockDriverState *bs)
+{
+    return bs->min_io_size;
+}
+
+void bdrv_set_min_io_size(BlockDriverState *bs,
+        unsigned int min_io_size)
+{
+    bs->min_io_size = min_io_size;
+}
+
+unsigned int bdrv_get_opt_io_size(BlockDriverState *bs)
+{
+    return bs->opt_io_size;
+}
+
+void bdrv_set_opt_io_size(BlockDriverState *bs,
+        unsigned int opt_io_size)
+{
+    bs->opt_io_size = opt_io_size;
+}
+
 /* XXX: no longer used */
 void bdrv_set_change_cb(BlockDriverState *bs,
                         void (*change_cb)(void *opaque), void *opaque)
Index: qemu/block.h
===================================================================
--- qemu.orig/block.h	2010-01-29 11:07:50.089004011 +0100
+++ qemu/block.h	2010-01-29 11:08:32.940004255 +0100
@@ -152,6 +152,16 @@ int bdrv_is_inserted(BlockDriverState *b
 int bdrv_media_changed(BlockDriverState *bs);
 int bdrv_is_locked(BlockDriverState *bs);
 void bdrv_set_locked(BlockDriverState *bs, int locked);
+unsigned int bdrv_get_physical_block_size(BlockDriverState *bs);
+unsigned int bdrv_get_physical_block_exp(BlockDriverState *bs);
+void bdrv_set_physical_block_size(BlockDriverState *bs,
+        unsigned int physical_block_size);
+unsigned int bdrv_get_min_io_size(BlockDriverState *bs);
+void bdrv_set_min_io_size(BlockDriverState *bs,
+        unsigned int min_io_size);
+unsigned int bdrv_get_opt_io_size(BlockDriverState *bs);
+void bdrv_set_opt_io_size(BlockDriverState *bs,
+        unsigned int opt_io_size);
 int bdrv_eject(BlockDriverState *bs, int eject_flag);
 void bdrv_set_change_cb(BlockDriverState *bs,
                         void (*change_cb)(void *opaque), void *opaque);
Index: qemu/block_int.h
===================================================================
--- qemu.orig/block_int.h	2010-01-29 11:07:50.096004065 +0100
+++ qemu/block_int.h	2010-01-29 11:08:32.941003474 +0100
@@ -173,6 +173,14 @@ struct BlockDriverState {
        drivers. They are not used by the block driver */
     int cyls, heads, secs, translation;
     int type;
+
+    /*
+     * Topology information, all optional.
+     */
+    unsigned int physical_block_size;
+    unsigned int min_io_size;
+    unsigned int opt_io_size;
+
     char device_name[32];
     unsigned long *dirty_bitmap;
     BlockDriverState *next;
Index: qemu/qemu-config.c
===================================================================
--- qemu.orig/qemu-config.c	2010-01-29 11:07:50.133004032 +0100
+++ qemu/qemu-config.c	2010-01-29 11:08:32.944025367 +0100
@@ -78,6 +78,15 @@ QemuOptsList qemu_drive_opts = {
         },{
             .name = "readonly",
             .type = QEMU_OPT_BOOL,
+        },{
+            .name = "physical_block_size",
+            .type = QEMU_OPT_NUMBER,
+        },{
+            .name = "min_io_size",
+            .type = QEMU_OPT_NUMBER,
+        },{
+            .name = "opt_io_size",
+            .type = QEMU_OPT_NUMBER,
         },
         { /* end if list */ }
     },
Index: qemu/vl.c
===================================================================
--- qemu.orig/vl.c	2010-01-29 11:07:50.141004284 +0100
+++ qemu/vl.c	2010-01-29 11:08:32.947003820 +0100
@@ -1904,6 +1904,9 @@ DriveInfo *drive_init(QemuOpts *opts, vo
     int index;
     int cache;
     int aio = 0;
+    unsigned long physical_block_size = 512;
+    unsigned long min_io_size = 0;
+    unsigned long opt_io_size = 0;
     int ro = 0;
     int bdrv_flags;
     int on_read_error, on_write_error;
@@ -2053,6 +2056,32 @@ DriveInfo *drive_init(QemuOpts *opts, vo
     }
 #endif
 
+    if ((buf = qemu_opt_get(opts, "physical_block_size")) != NULL) {
+        physical_block_size = strtoul(buf, NULL, 10);
+        if (physical_block_size < 512) {
+            fprintf(stderr, "sector size must be larger than 512 bytes\n");
+            return NULL;
+        }
+    }
+
+    if ((buf = qemu_opt_get(opts, "min_io_size")) != NULL) {
+        min_io_size = strtoul(buf, NULL, 10);
+        if (!min_io_size || (min_io_size % physical_block_size)) {
+            fprintf(stderr,
+                    "min_io_size must be a multiple of the sector size\n");
+            return NULL;
+        }
+    }
+
+    if ((buf = qemu_opt_get(opts, "opt_io_size")) != NULL) {
+        opt_io_size = strtoul(buf, NULL, 10);
+        if (!opt_io_size || (opt_io_size % min_io_size)) {
+            fprintf(stderr,
+                    "opt_io_size must be a multiple of min_io_size\n");
+            return NULL;
+        }
+    }
+
     if ((buf = qemu_opt_get(opts, "format")) != NULL) {
        if (strcmp(buf, "?") == 0) {
             fprintf(stderr, "qemu: Supported formats:");
@@ -2257,6 +2286,12 @@ DriveInfo *drive_init(QemuOpts *opts, vo
         return NULL;
     }
 
+    bdrv_set_physical_block_size(dinfo->bdrv, physical_block_size);
+    if (min_io_size)
+        bdrv_set_min_io_size(dinfo->bdrv, min_io_size);
+    if (opt_io_size)
+        bdrv_set_opt_io_size(dinfo->bdrv, opt_io_size);
+
     if (bdrv_key_required(dinfo->bdrv))
         autostart = 0;
     *fatal_error = 0;
Index: qemu/qemu-options.hx
===================================================================
--- qemu.orig/qemu-options.hx	2010-01-29 11:07:50.149004395 +0100
+++ qemu/qemu-options.hx	2010-01-29 19:36:06.118256061 +0100
@@ -104,6 +104,7 @@ DEF("drive", HAS_ARG, QEMU_OPTION_drive,
     "       [,cyls=c,heads=h,secs=s[,trans=t]][,snapshot=on|off]\n"
     "       [,cache=writethrough|writeback|none][,format=f][,serial=s]\n"
     "       [,addr=A][,id=name][,aio=threads|native][,readonly=on|off]\n"
+    "       [,physical_block=size=size][,min_io_size=size][,opt_io_size=size]\n"
     "                use 'file' as a drive image\n")
 DEF("set", HAS_ARG, QEMU_OPTION_set,
     "-set group.id.arg=value\n"
@@ -149,6 +150,15 @@ an untrusted format header.
 This option specifies the serial number to assign to the device.
 @item addr=@var{addr}
 Specify the controller's PCI address (if=virtio only).
+@item physical_sector_size=@var{size}
+Report a physical block size larger than the logical block size of 512 bytes.
+@item min_io_size=@var{size}
+Reported a minimum I/O size or optimum I/O granularity.  This is the smallest
+I/O size the device can perform without a performance penalty.  For RAID
+devices this should be set to the stripe chunk size.
+@item opt_io_size=@var{size}
+Report an optimal I/O size, which is the device's preferred unit for
+sustained I/O.  This should be set to the stripe width for RAID devices.
 @end table
 
 By default, writethrough caching is used for all block device.  This means that