[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index] Re: [PATCH v3 13/28] hw/xen: automatically assign device index to block devices
On Fri, 2023-10-27 at 11:32 +0100, Durrant, Paul wrote: > On 27/10/2023 11:25, David Woodhouse wrote: > > On Fri, 2023-10-27 at 10:01 +0100, Durrant, Paul wrote: > > > > > > This code is allocating a name automatically so I think the onus is on > > > it not create a needless clash which is likely to have unpredictable > > > results depending on what the guest is. Just avoid any aliasing in the > > > first place and things will be fine. > > > > > > Yeah, fair enough. In which case I'll probably switch to using > > xs_directory() and then processing those results to find a free slot, > > instead of going out to XenStore for every existence check. > > > > This isn't exactly fast path and I'm prepared to tolerate a little bit > > of O(n²), but only within reason :) > > Yes, doing an xs_directory() and then using the code > xen_block_get_vdev() to populate a list of existent disks will be neater. diff --git a/hw/block/xen-block.c b/hw/block/xen-block.c index 5011fe9430..9b7d7ef7e1 100644 --- a/hw/block/xen-block.c +++ b/hw/block/xen-block.c @@ -30,48 +30,105 @@ #include "hw/xen/interface/io/xs_wire.h" #include "trace.h" -static char *xen_block_get_name(XenDevice *xendev, Error **errp) +#define XVDA_MAJOR 202 +#define XVDQ_MAJOR (1<<20) +#define XVDBGQCV_MAJOR ((1<<21) - 1) +#define HDA_MAJOR 3 +#define HDC_MAJOR 22 +#define SDA_MAJOR 8 + +/* + * This is fairly arbitrary just to avoid a stupidly sized bitmap, but Linux + * as of v6.6 only supports up to /dev/xvdfan (disk 4095) anyway. + */ +#define MAX_AUTO_VDEV 4096 + +static int vdev_to_diskno(unsigned int vdev_nr) { - XenBlockDevice *blockdev = XEN_BLOCK_DEVICE(xendev); + switch (vdev_nr >> 8) { + case XVDA_MAJOR: + case SDA_MAJOR: + return (vdev_nr >> 4) & 0x15; + + case HDA_MAJOR: + return (vdev_nr >> 6) & 1; + + case HDC_MAJOR: + return ((vdev_nr >> 6) & 1) + 2; + + case XVDQ_MAJOR ... XVDBGQCV_MAJOR: + return (vdev_nr >> 8) & 0xfffff; + + default: + return -1; + } +} + +static bool xen_block_find_free_vdev(XenBlockDevice *blockdev, Error **errp) +{ + XenBus *xenbus = XEN_BUS(qdev_get_parent_bus(DEVICE(blockdev))); + unsigned long used_devs[BITS_TO_LONGS(MAX_AUTO_VDEV)]; XenBlockVdev *vdev = &blockdev->props.vdev; + char fe_path[XENSTORE_ABS_PATH_MAX + 1]; + char **existing_frontends; + unsigned int nr_existing = 0; + unsigned int vdev_nr; + int i, disk = 0; + + snprintf(fe_path, sizeof(fe_path), "/local/domain/%u/device/vbd", + blockdev->xendev.frontend_id); + + existing_frontends = qemu_xen_xs_directory(xenbus->xsh, XBT_NULL, fe_path, + &nr_existing); + if (!existing_frontends && errno != ENOENT) { + error_setg_errno(errp, errno, "cannot read %s", fe_path); + return false; + } - 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 */ - 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++; + memset(used_devs, 0, sizeof(used_devs)); + for (i = 0; i < nr_existing; i++) { + if (qemu_strtoui(existing_frontends[i], NULL, 10, &vdev_nr)) { + free(existing_frontends[i]); + continue; } + + free(existing_frontends[i]); + + disk = vdev_to_diskno(vdev_nr); + if (disk < 0 || disk >= MAX_AUTO_VDEV) { + continue; + } + + set_bit(disk, used_devs); + } + free(existing_frontends); + + disk = find_first_zero_bit(used_devs, MAX_AUTO_VDEV); + if (disk == MAX_AUTO_VDEV) { error_setg(errp, "cannot find device vdev for block device"); + return false; + } + + vdev->type = XEN_BLOCK_VDEV_TYPE_XVD; + vdev->partition = 0; + vdev->disk = disk; + if (disk < (1 << 4)) { + vdev->number = (XVDA_MAJOR << 8) | (disk << 4); + } else { + vdev->number = (XVDQ_MAJOR << 8) | (disk << 8); + } + return true; +} + +static char *xen_block_get_name(XenDevice *xendev, Error **errp) +{ + XenBlockDevice *blockdev = XEN_BLOCK_DEVICE(xendev); + XenBlockVdev *vdev = &blockdev->props.vdev; + + if (vdev->type == XEN_BLOCK_VDEV_TYPE_INVALID && + !xen_block_find_free_vdev(blockdev, errp)) { return NULL; } - found: return g_strdup_printf("%lu", vdev->number); } @@ -520,10 +577,10 @@ static void xen_block_set_vdev(Object *obj, Visitor *v, const char *name, case XEN_BLOCK_VDEV_TYPE_DP: case XEN_BLOCK_VDEV_TYPE_XVD: if (vdev->disk < (1 << 4) && vdev->partition < (1 << 4)) { - vdev->number = (202 << 8) | (vdev->disk << 4) | + vdev->number = (XVDA_MAJOR << 8) | (vdev->disk << 4) | vdev->partition; } else if (vdev->disk < (1 << 20) && vdev->partition < (1 << 8)) { - vdev->number = (1 << 28) | (vdev->disk << 8) | + vdev->number = (XVDQ_MAJOR << 8) | (vdev->disk << 8) | vdev->partition; } else { goto invalid; @@ -533,10 +590,10 @@ static void xen_block_set_vdev(Object *obj, Visitor *v, const char *name, case XEN_BLOCK_VDEV_TYPE_HD: if ((vdev->disk == 0 || vdev->disk == 1) && vdev->partition < (1 << 6)) { - vdev->number = (3 << 8) | (vdev->disk << 6) | vdev->partition; + vdev->number = (HDA_MAJOR << 8) | (vdev->disk << 6) | vdev->partition; } else if ((vdev->disk == 2 || vdev->disk == 3) && vdev->partition < (1 << 6)) { - vdev->number = (22 << 8) | ((vdev->disk - 2) << 6) | + vdev->number = (HDC_MAJOR << 8) | ((vdev->disk - 2) << 6) | vdev->partition; } else { goto invalid; @@ -545,7 +602,7 @@ static void xen_block_set_vdev(Object *obj, Visitor *v, const char *name, case XEN_BLOCK_VDEV_TYPE_SD: if (vdev->disk < (1 << 4) && vdev->partition < (1 << 4)) { - vdev->number = (8 << 8) | (vdev->disk << 4) | vdev->partition; + vdev->number = (SDA_MAJOR << 8) | (vdev->disk << 4) | vdev->partition; } else { goto invalid; } Attachment:
smime.p7s
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