Re: [PATCH v3 13/28] hw/xen: automatically assign device index to block devices

["Durrant, Paul" <xadimgnik@gmail.com>]

On 25/10/2023 15:50, David Woodhouse wrote:
> From: David Woodhouse <dwmw@amazon.co.uk>
> 
> There's no need to force the user to assign a vdev. We can automatically
> assign one, starting at xvda and searching until we find the first disk
> name that's unused.
> 
> This means we can now allow '-drive if=xen,file=xxx' to work without an
> explicit separate -driver argument, just like if=virtio.
> 
> Rip out the legacy handling from the xenpv machine, which was scribbling
> over any disks configured by the toolstack, and didn't work with anything
> but raw images.
> 
> Signed-off-by: David Woodhouse <dwmw@amazon.co.uk>
> Acked-by: Kevin Wolf <kwolf@redhat.com>
> ---
>   blockdev.c                          | 15 +++++++++---
>   hw/block/xen-block.c                | 38 +++++++++++++++++++++++++++++
>   hw/xen/xen_devconfig.c              | 28 ---------------------
>   hw/xenpv/xen_machine_pv.c           |  9 -------
>   include/hw/xen/xen-legacy-backend.h |  1 -
>   5 files changed, 50 insertions(+), 41 deletions(-)
> 
> diff --git a/blockdev.c b/blockdev.c
> index a01c62596b..5d9f2e5395 100644
> --- a/blockdev.c
> +++ b/blockdev.c
> @@ -255,13 +255,13 @@ void drive_check_orphaned(void)
>            * Ignore default drives, because we create certain default
>            * drives unconditionally, then leave them unclaimed.  Not the
>            * users fault.
> -         * Ignore IF_VIRTIO, because it gets desugared into -device,
> -         * so we can leave failing to -device.
> +         * Ignore IF_VIRTIO or IF_XEN, because it gets desugared into
> +         * -device, so we can leave failing to -device.
>            * Ignore IF_NONE, because leaving unclaimed IF_NONE remains
>            * available for device_add is a feature.
>            */
>           if (dinfo->is_default || dinfo->type == IF_VIRTIO
> -            || dinfo->type == IF_NONE) {
> +            || dinfo->type == IF_XEN || dinfo->type == IF_NONE) {
>               continue;
>           }
>           if (!blk_get_attached_dev(blk)) {
> @@ -977,6 +977,15 @@ DriveInfo *drive_new(QemuOpts *all_opts, BlockInterfaceType block_default_type,
>           qemu_opt_set(devopts, "driver", "virtio-blk", &error_abort);
>           qemu_opt_set(devopts, "drive", qdict_get_str(bs_opts, "id"),
>                        &error_abort);
> +    } else if (type == IF_XEN) {
> +        QemuOpts *devopts;
> +        devopts = qemu_opts_create(qemu_find_opts("device"), NULL, 0,
> +                                   &error_abort);
> +        qemu_opt_set(devopts, "driver",
> +                     (media == MEDIA_CDROM) ? "xen-cdrom" : "xen-disk",
> +                     &error_abort);
> +        qemu_opt_set(devopts, "drive", qdict_get_str(bs_opts, "id"),
> +                     &error_abort);
>       }
>   
>       filename = qemu_opt_get(legacy_opts, "file");
> diff --git a/hw/block/xen-block.c b/hw/block/xen-block.c
> index 64470fc579..5011fe9430 100644
> --- a/hw/block/xen-block.c
> +++ b/hw/block/xen-block.c
> @@ -27,6 +27,7 @@
>   #include "sysemu/block-backend.h"
>   #include "sysemu/iothread.h"
>   #include "dataplane/xen-block.h"
> +#include "hw/xen/interface/io/xs_wire.h"
>   #include "trace.h"
>   
>   static char *xen_block_get_name(XenDevice *xendev, Error **errp)
> @@ -34,6 +35,43 @@ static char *xen_block_get_name(XenDevice *xendev, Error **errp)
>       XenBlockDevice *blockdev = XEN_BLOCK_DEVICE(xendev);
>       XenBlockVdev *vdev = &blockdev->props.vdev;
>   
> +    if (blockdev->props.vdev.type == XEN_BLOCK_VDEV_TYPE_INVALID) {
> +        XenBus *xenbus = XEN_BUS(qdev_get_parent_bus(DEVICE(xendev)));
> +        char fe_path[XENSTORE_ABS_PATH_MAX + 1];
> +        char *value;
> +        int disk = 0;
> +        unsigned long idx;
> +
> +        /* Find an unoccupied device name */

Not sure this is going to work is it? What happens if 'hda' or 'sda', or 
'd0' exists? I think you need to use the core of the code in 
xen_block_set_vdev() to generate names and search all possible encodings 
for each disk.

   Paul

> +        while (disk < (1 << 20)) {
> +            if (disk < (1 << 4)) {
> +                idx = (202 << 8) | (disk << 4);
> +            } else {
> +                idx = (1 << 28) | (disk << 8);
> +            }
> +            snprintf(fe_path, sizeof(fe_path),
> +                     "/local/domain/%u/device/vbd/%lu",
> +                     xendev->frontend_id, idx);
> +            value = qemu_xen_xs_read(xenbus->xsh, XBT_NULL, fe_path, NULL);
> +            if (!value) {
> +                if (errno == ENOENT) {
> +                    vdev->type = XEN_BLOCK_VDEV_TYPE_XVD;
> +                    vdev->partition = 0;
> +                    vdev->disk = disk;
> +                    vdev->number = idx;
> +                    goto found;
> +                }
> +                error_setg(errp, "cannot read %s: %s", fe_path,
> +                           strerror(errno));
> +                return NULL;
> +            }
> +            free(value);
> +            disk++;
> +        }
> +        error_setg(errp, "cannot find device vdev for block device");
> +        return NULL;
> +    }
> + found:
>       return g_strdup_printf("%lu", vdev->number);
>   }
>   
> diff --git a/hw/xen/xen_devconfig.c b/hw/xen/xen_devconfig.c
> index 9b7304e544..3f77c675c6 100644
> --- a/hw/xen/xen_devconfig.c
> +++ b/hw/xen/xen_devconfig.c
> @@ -46,34 +46,6 @@ static int xen_config_dev_all(char *fe, char *be)
>   
>   /* ------------------------------------------------------------- */
>   
> -int xen_config_dev_blk(DriveInfo *disk)
> -{
> -    char fe[256], be[256], device_name[32];
> -    int vdev = 202 * 256 + 16 * disk->unit;
> -    int cdrom = disk->media_cd;
> -    const char *devtype = cdrom ? "cdrom" : "disk";
> -    const char *mode    = cdrom ? "r"     : "w";
> -    const char *filename = qemu_opt_get(disk->opts, "file");
> -
> -    snprintf(device_name, sizeof(device_name), "xvd%c", 'a' + disk->unit);
> -    xen_pv_printf(NULL, 1, "config disk %d [%s]: %s\n",
> -                  disk->unit, device_name, filename);
> -    xen_config_dev_dirs("vbd", "qdisk", vdev, fe, be, sizeof(fe));
> -
> -    /* frontend */
> -    xenstore_write_int(fe, "virtual-device",  vdev);
> -    xenstore_write_str(fe, "device-type",     devtype);
> -
> -    /* backend */
> -    xenstore_write_str(be, "dev",             device_name);
> -    xenstore_write_str(be, "type",            "file");
> -    xenstore_write_str(be, "params",          filename);
> -    xenstore_write_str(be, "mode",            mode);
> -
> -    /* common stuff */
> -    return xen_config_dev_all(fe, be);
> -}
> -
>   int xen_config_dev_nic(NICInfo *nic)
>   {
>       char fe[256], be[256];
> diff --git a/hw/xenpv/xen_machine_pv.c b/hw/xenpv/xen_machine_pv.c
> index 17cda5ec13..1533f5dfb4 100644
> --- a/hw/xenpv/xen_machine_pv.c
> +++ b/hw/xenpv/xen_machine_pv.c
> @@ -32,7 +32,6 @@
>   
>   static void xen_init_pv(MachineState *machine)
>   {
> -    DriveInfo *dinfo;
>       int i;
>   
>       setup_xen_backend_ops();
> @@ -64,14 +63,6 @@ static void xen_init_pv(MachineState *machine)
>           vga_interface_created = true;
>       }
>   
> -    /* configure disks */
> -    for (i = 0; i < 16; i++) {
> -        dinfo = drive_get(IF_XEN, 0, i);
> -        if (!dinfo)
> -            continue;
> -        xen_config_dev_blk(dinfo);
> -    }
> -
>       /* configure nics */
>       for (i = 0; i < nb_nics; i++) {
>           if (!nd_table[i].model || 0 != strcmp(nd_table[i].model, "xen"))
> diff --git a/include/hw/xen/xen-legacy-backend.h b/include/hw/xen/xen-legacy-backend.h
> index 6c307c5f2c..fc42146bc2 100644
> --- a/include/hw/xen/xen-legacy-backend.h
> +++ b/include/hw/xen/xen-legacy-backend.h
> @@ -81,7 +81,6 @@ extern struct XenDevOps xen_usb_ops;          /* xen-usb.c         */
>   
>   /* configuration (aka xenbus setup) */
>   void xen_config_cleanup(void);
> -int xen_config_dev_blk(DriveInfo *disk);
>   int xen_config_dev_nic(NICInfo *nic);
>   int xen_config_dev_vfb(int vdev, const char *type);
>   int xen_config_dev_vkbd(int vdev);