/* This is the PCI capability header: */
struct virtio_pci_cap {__u8 cap_vndr; /* Generic PCI field: PCI_CAP_ID_VNDR */__u8 cap_next; /* Generic PCI field: next ptr. */__u8 cap_len; /* Generic PCI field: capability length */__u8 cfg_type; /* Identifies the structure. */__u8 bar; /* Where to find it. */__u8 id; /* Multiple capabilities of the same type */__u8 padding[2]; /* Pad to full dword. */__le32 offset; /* Offset within bar. */__le32 length; /* Length of the structure, in bytes. */
};
从上可知，迁移的virtio设备，由于源端上BAR0地址的bit[4,7]内容为0xc，目的端BAR0地址的bit[4,7]内容为0，分析目的端日志： 2023-09-15T04:52:39.221154Z qemu-kvm: error while loading state for instance 0x0 of device ‘0000:00:0b.0/virtio-blk’ 迁移的设备是1个磁盘设备，其bdf号为00:0b.0，对比源端的virtio-pci设备：
Bus 0, device 11, function 0:SCSI controller: PCI device 1af4:1001IRQ 0.BAR0: I/O at 0xffc0 [0xffff].BAR1: 32 bit memory at 0xfebff000 [0xfebfffff].BAR4: 64 bit prefetchable memory at 0x4287fffc000 [0x4287fffffff].id "virtio-disk1"
Bus 0, device 11, function 0:SCSI controller: PCI device 1af4:1001IRQ 0.BAR0: I/O at 0xd080 [0xd0ff].BAR1: 32 bit memory at 0xfea9a000 [0xfea9afff].BAR4: 64 bit prefetchable memory at 0xfe210000 [0xfe213fff].id "virtio-disk1"
37b06f8d46 virtio-blk: add DISCARD and WRITE_ZEROES features
20764be042 virtio-blk: set config size depending on the features enabled
ba550851f5 virtio-net: make VirtIOFeature usable for other virtio devices
5c81161f80 virtio-blk: add "discard" and "write-zeroes" properties
bbe8bd4d85 virtio-blk: add host_features field in VirtIOBlock
00f639fb8f virtio-blk: add acct_failed param to virtio_blk_handle_rw_error
struct virtio_blk_config {/* The capacity (in 512-byte sectors). */uint64_t capacity;/* The maximum segment size (if VIRTIO_BLK_F_SIZE_MAX) */uint32_t size_max;/* The maximum number of segments (if VIRTIO_BLK_F_SEG_MAX) */uint32_t seg_max;/* geometry of the device (if VIRTIO_BLK_F_GEOMETRY) */struct virtio_blk_geometry {uint16_t cylinders;uint8_t heads;uint8_t sectors;} geometry;/* block size of device (if VIRTIO_BLK_F_BLK_SIZE) */uint32_t blk_size;/* the next 4 entries are guarded by VIRTIO_BLK_F_TOPOLOGY *//* exponent for physical block per logical block. */uint8_t physical_block_exp;/* alignment offset in logical blocks. */uint8_t alignment_offset;/* minimum I/O size without performance penalty in logical blocks. */uint16_t min_io_size;/* optimal sustained I/O size in logical blocks. */uint32_t opt_io_size;/* writeback mode (if VIRTIO_BLK_F_CONFIG_WCE) */uint8_t wce;uint8_t unused;/* number of vqs, only available when VIRTIO_BLK_F_MQ is set */uint16_t num_queues;
}
+
+ /* the next 3 entries are guarded by VIRTIO_BLK_F_DISCARD */
+ /*
+ * The maximum discard sectors (in 512-byte sectors) for
+ * one segment.
+ */
+ uint32_t max_discard_sectors;
+ /*
+ * The maximum number of discard segments in a
+ * discard command.
+ */
+ uint32_t max_discard_seg;
+ /* Discard commands must be aligned to this number of sectors. */
+ uint32_t discard_sector_alignment;
+
+ /* the next 3 entries are guarded by VIRTIO_BLK_F_WRITE_ZEROES */
+ /*
+ * The maximum number of write zeroes sectors (in 512-byte sectors) in
+ * one segment.
+ */
+ uint32_t max_write_zeroes_sectors;
+ /*
+ * The maximum number of segments in a write zeroes
+ * command.
+ */
+ uint32_t max_write_zeroes_seg;
+ /*
+ * Set if a VIRTIO_BLK_T_WRITE_ZEROES request may result in the
+ * deallocation of one or more of the sectors.
+ */
+ uint8_t write_zeroes_may_unmap;
+
+ uint8_t unused1[3];
前言： 90年代初，微软出了Quick系统对抗Borland Turbo系列，其中包括 QuickBasic, QuickPascal和Quick C。1991年，Quick C for Windows 1.0发布，后来它被Visual C取代。我自己觉得微软成就在那个winstub.exe桩上…
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