virtio 是一種 I/O 半虛擬化解決方案，是一套通用 I/O 設(shè)備虛擬化的程序，是對半虛擬化 Hypervisor 中的一組通用 I/O 設(shè)備的抽象。對比其他設(shè)備有宿主計算機(jī)模擬，virtio設(shè)備效率更高。

virtio架構(gòu)圖：

最上面一排是不同的設(shè)備，如塊設(shè)備，網(wǎng)絡(luò)設(shè)備，控制臺等

virtio 層屬于控制層，負(fù)責(zé)設(shè)備跟宿主OS之間的通知機(jī)制（kick，notify）和控制流程，而 virtio-vring 則負(fù)責(zé)具體數(shù)據(jù)流轉(zhuǎn)發(fā)。

vring 包含三個部分，描述符數(shù)組 desc，可用的 available ring 和使用過的 used ring。

struct vring_desc {/* Address (guest-physical). */u64 addr;/* Length. */u32 len;/* The flags as indicated above. */u16 flags;/* We chain unused descriptors via this, too */u16 next; };

vring描述符結(jié)構(gòu)。

struct vring_avail {u16 flags;u16 idx;u16 ring[]; }; struct vring_used_elem {/* Index of start of used descriptor chain. */u32 id;/* Total length of the descriptor chain which was used (written to) */u32 len; };struct vring_used {u16 flags;u16 idx;struct vring_used_elem ring[]; };

avail跟used結(jié)構(gòu)。

static inline void vring_init(struct vring *vr, unsigned int num, void *p,unsigned long align) {vr->num = num;vr->desc = p;vr->avail = (void *)((char *)p + num*sizeof(struct vring_desc));vr->used = (void *)(((unsigned long)&vr->avail->ring[num] + sizeof(u16)+ align-1) & ~(align - 1)); }static inline unsigned vring_size(unsigned int num, unsigned long align) {return ((sizeof(struct vring_desc) * num + sizeof(u16) * (3 + num)+ align - 1) & ~(align - 1))+ sizeof(u16) * 3 + sizeof(struct vring_used_elem) * num; }

vring_size計算vring需要的內(nèi)存大小，num是vring的描述符數(shù)量，為2^N，如128，256，512等。

首先放的是num個描述符vring_desc，然后是vring_avail，在vring_avail結(jié)尾有個16字位的used_event，因此是是（3+num）。之后放得是vring_used，同樣，后面有個16位的avail_event，因此也是sizeof(u16) * 3。

vring_used需要4K對齊。

used_event用來通知宿主os，讀取到哪里了。avail_event用來通知宿主os，寫到哪里了。

設(shè)置avail_event，用來通知宿主os有新命令需要處理。宿主os完成之后產(chǎn)生中斷，處理完成之后設(shè)置used_event，表示數(shù)據(jù)處理過了，這樣宿主os才會有數(shù)據(jù)的時候繼續(xù)發(fā)生中斷。

desc 用于存儲一些關(guān)聯(lián)的描述符，每個描述符記錄一個對 buffer 的描述，available ring 則用于 guest 端表示當(dāng)前有哪些描述符是可用的，而 used ring 則表示 host 端哪些描述符已經(jīng)被使用。

Virtio 使用 virtqueue 來實(shí)現(xiàn) I/O 機(jī)制，每個 virtqueue 就是一個承載大量數(shù)據(jù)的隊(duì)列，具體使用多少個隊(duì)列取決于需求，例如，virtio 網(wǎng)絡(luò)驅(qū)動程序（virtio-net）使用兩個隊(duì)列（一個用于接受，另一個用于發(fā)送），而 virtio 塊驅(qū)動程序（virtio-blk）僅使用一個隊(duì)列。

比如讀取硬盤。取得virtqueue隊(duì)列，virtio-blk就一個隊(duì)列。然后往里面添加3條結(jié)構(gòu)化數(shù)據(jù)。

struct addr_size {unsigned long vp_addr; /* 物理地址 */u32 vp_size; /* 大小 */u32 vp_flag; /*標(biāo)記，如讀，寫*/ };

第一條是請求命令數(shù)據(jù)：

struct blk_outhdr {/* VIRTIO_BLK_T* */u32 type;/* io priority. */u32 ioprio;/* Sector (ie. 512 byte offset) */u64 sector;};

告訴驅(qū)動是讀還是寫（type），優(yōu)先級，扇區(qū)號。

第二條是輸出緩沖區(qū)，即扇區(qū)讀取到哪里，緩沖區(qū)大小。

第三條就1個字節(jié)，用來指示操作結(jié)果，0表示成功。

module/blk/virtio_blk.c

struct blk_req {struct blk_outhdr hdr;uchar status; }; static struct blk_req rq; static void virtio_blk_read(ulong sector) {struct addr_size phys[3];rq.hdr.type = VIRTIO_BLK_T_IN;rq.hdr.ioprio = 0;rq.hdr.sector = sector;phys[0].vp_addr = V2P((ulong)&rq.hdr);phys[0].vp_size = sizeof(rq.hdr);phys[0].vp_flag = VRING_DESC_F_READ;phys[1].vp_addr = V2P((ulong)buf);phys[1].vp_size = 512;phys[1].vp_flag = VRING_DESC_F_WRITE;uchar status = 0;phys[2].vp_addr = V2P((ulong)&rq.status);phys[2].vp_size = sizeof(status);pyhs[2].vp_flag = VRING_DESC_F_WRITE;virtio_to_queue(to_virtio_dev_t(&pci_vblk), 0, phys, 3, &rq);}

virtio_to_queue把3個描述符寫入vring，然后kick通知宿主os。

libs/libvirtio/virtio.c

int virtio_to_queue(virtio_dev_t dev, int qidx, struct addr_size *bufs,size_t num, void *data) {u16_t free_first;int left;struct virtio_queue *q = &dev->queues[qidx];struct vring *vring = &q->vring;ASSERT(0 <= qidx && qidx <= dev->num_queues);if (!data)panic("%s: NULL data received queue %d", __func__, qidx);free_first = q->free_head;left = (int)q->free_num - (int)num;pci_d("free_first:%016lx,left:%d,dev->threads:%d,n:%dn",free_first,left, dev->threads,num);if (left < dev->threads)set_indirect_descriptors(dev, q, bufs, num);elseset_direct_descriptors(q, bufs, num);/* Next index for host is old free_head */vring->avail->ring[vring->avail->idx % q->num] = free_first;/* Provided by the caller to identify this slot */q->data[free_first] = data;/* Make sure the host sees the new descriptors */virtio_wmb(true);/* advance last idx */vring->avail->idx += 1;/* Make sure the host sees the avail->idx */virtio_rmb(true);/* kick it! */kick_queue(dev, qidx);return 0; }

kick_queue通知宿主os進(jìn)行處理。

void *data為驅(qū)動數(shù)據(jù)，到時候宿主os完成之后通知驅(qū)動調(diào)用virtio_from_queue會返回。

這里為struct blk_req rq; 目前比較簡單，就一個狀態(tài)跟hdr請求結(jié)構(gòu)。狀態(tài)為第三個描述符：

phys[2].vp_addr = V2P((ulong)&rq.status);phys[2].vp_size = sizeof(status);pyhs[2].vp_flag = VRING_DESC_F_WRITE;

由宿主os填寫是否操作成功。

int virtio_from_queue(virtio_dev_t dev, int qidx, void **data, size_t * len) {struct virtio_queue *q;struct vring *vring;struct vring_used_elem *uel;struct vring_desc *vd;int count = 0;u16_t idx;u16_t used_idx;ASSERT(0 <= qidx && qidx < dev->num_queues);q = &dev->queues[qidx];vring = &q->vring;/* Make sure we see changes done by the host */virtio_rmb(true);/* The index from the host */used_idx = vring->used->idx % q->num;/* We already saw this one, nothing to do here */if (q->last_used == used_idx)return -1;/* Get the vring_used element */uel = &q->vring.used->ring[q->last_used];/* Update the last used element */q->last_used = (q->last_used + 1) % q->num;/* index of the used element */idx = uel->id % q->num;ASSERT(q->data[idx] != NULL);/* Get the descriptor */vd = &vring->desc[idx];/* Unconditionally set the tail->next to the first used one */ASSERT(vring->desc[q->free_tail].flags & VRING_DESC_F_NEXT);vring->desc[q->free_tail].next = idx;/* Find the last index, eventually there has to be one* without a the next flag.** FIXME: Protect from endless loop*/while (vd->flags & VRING_DESC_F_NEXT) {if (vd->flags & VRING_DESC_F_INDIRECT)clear_indirect_table(dev, vd);idx = vd->next;vd = &vring->desc[idx];count++;}/* Didn't count the last one */count++;if (vd->flags & VRING_DESC_F_INDIRECT)clear_indirect_table(dev, vd);/* idx points to the tail now, update the queue */q->free_tail = idx;ASSERT(!(vd->flags & VRING_DESC_F_NEXT));/* We can always connect the tail with the head */vring->desc[q->free_tail].next = q->free_head;vring->desc[q->free_tail].flags = VRING_DESC_F_NEXT;q->free_num += count;ASSERT(q->free_num <= q->num);*data = q->data[uel->id];q->data[uel->id] = NULL;if (len != NULL)*len = uel->len;q->last_used_idx++;if (!(vring->avail->flags & VRING_AVAIL_F_NO_INTERRUPT))virtio_store_mb(true,vring->used_event,q->last_used_idx);return 0; }

virtio_from_queue用于處理結(jié)果。

下面做個virtio_blk的實(shí)驗(yàn):

module/blk/virtio_blk.c

static void irq_handler(int n) {uchar isr =virtio_conf_readb(to_virtio_dev_t(&pci_vblk), VIRTIO_PCI_ISR);ack_lapic_irq();virtio_queue_disable_intr(virtio_get_queue(to_virtio_dev_t(&pci_vblk), 0));printk("****virtio_blk_irq_handler**** irq:%d,isr:%d cpu:%dn", n,isr,smp_processor_id());virtio_blk_check_queue(); } void virtio_blk_read_config(struct virtio_blk *p) {virtio_dev_t pvirtio = to_virtio_dev_t(p);u32 offset = virtio_pci_config_offset(to_virtio_dev_t(p));virtio_conf_read(pvirtio, offset, &p->_config,sizeof(p->_config));if (virtio_get_guest_feature_bit(to_virtio_dev_t(p), VIRTIO_BLK_F_SIZE_MAX)) {pci_d("VIRTIO_BLK_F_SIZE_MAX:%xn",p->_config.size_max);}if (virtio_get_guest_feature_bit(to_virtio_dev_t(p), VIRTIO_BLK_F_SEG_MAX)) {pci_d("VIRTIO_BLK_F_SEG_MAX:%xn",p->_config.seg_max);}if (virtio_get_guest_feature_bit(to_virtio_dev_t(p), VIRTIO_BLK_F_GEOMETRY)) {pci_d("VIRTIO_BLK cylinders:%x,heads:%x,sectors:%xn",p->_config.geometry.cylinders,p->_config.geometry.heads,p->_config.geometry.sectors);}if (virtio_get_guest_feature_bit(to_virtio_dev_t(p), VIRTIO_BLK_F_BLK_SIZE)) {pci_d("VIRTIO_BLK_F_BLK_SIZE:%xn",p->_config.blk_size);}if (virtio_get_guest_feature_bit(to_virtio_dev_t(p), VIRTIO_BLK_F_TOPOLOGY)) {pci_d("VIRTIO_BLK topology,physical_block_exp:%x,alignment:%x,min_io_size:%x,opt_io_size:%xn",p->_config.physical_block_exp,p->_config.alignment_offset,p->_config.min_io_size,p->_config.opt_io_size);}if (virtio_get_guest_feature_bit(to_virtio_dev_t(p), VIRTIO_BLK_F_CONFIG_WCE)) {pci_d("VIRTIO_BLK_F_WCE:%xn",p->_config.wce);}if (virtio_get_guest_feature_bit(to_virtio_dev_t(p), VIRTIO_BLK_F_RO)) {pci_d("VIRTIO_BLK readonlyn");}} static char buf[512]; struct blk_req {struct blk_outhdr hdr;pthread thread;uchar status; }; static struct blk_req rq; static void virtio_blk_read(ulong sector) {struct addr_size phys[3];rq.hdr.type = VIRTIO_BLK_T_IN;rq.hdr.ioprio = 0;rq.hdr.sector = sector;rq.thread = current;phys[0].vp_addr = V2P((ulong)&rq.hdr);phys[0].vp_size = sizeof(rq.hdr);phys[0].vp_flags = VRING_DESC_F_READ;phys[1].vp_addr = V2P((ulong)buf);phys[1].vp_size = 512;phys[1].vp_flags = VRING_DESC_F_WRITE;uchar status = 0;phys[2].vp_addr = V2P((ulong)&rq.status);phys[2].vp_size = sizeof(status);phys[2].vp_flags = VRING_DESC_F_WRITE;virtio_to_queue(to_virtio_dev_t(&pci_vblk), 0, phys, 3, &rq);suspend_thread();} static void virtio_blk_check_queue(void) {struct blk_req *p;size_t len;/* Put the received packets into the recv list */while (virtio_from_queue(to_virtio_dev_t(&pci_vblk),0 , (void **)&p, &len)== 0) {pci_d("virtio_blk_from_queue:%lx,len:%x,status:%d,thread:%sn", p, len,p->status,p->thread->name);wake_up_thread(p->thread);}} int init_virtio_blk() {virtio_dev_t dev = to_virtio_dev_t(&pci_vblk);if (virtio_setup_device(dev, VIRTIO_BLK_DEVICE_ID, 1)) {virtio_blk_read_config(&pci_vblk);//virtio_driver_init(dev);pci_dump_config(to_pci_device_t(&pci_vblk));msi_register_one(to_pci_device_t(&pci_vblk),0,irq_handler);virtio_device_ready(to_virtio_dev_t(&pci_vblk));memset(buf,0x12,512);//set_timeout_nsec(1000000000UL, vblk_timeout,dev);virtio_blk_read(1);dump_mem(buf,512);virtio_blk_read(1);dump_mem(buf,512);}return OK; } DECLARE_MODULE(virtio_blk_drivers, 0, main);

virtio_blk_read發(fā)送讀取命令之后就suspend_thread掛起當(dāng)前線程。

在中斷處理中如果讀取到數(shù)據(jù)，virtio_blk_check_queue，就恢復(fù)掛起的線程。

先把buf內(nèi)容設(shè)置為0x12，然后讀取內(nèi)容，打印內(nèi)存。

讀取2次是測試中斷是否正常。即第一次讀取之后要通知used_event，否則第二次讀取的時候不會發(fā)生中斷，但是如果去檢測隊(duì)列，是可以讀取到內(nèi)容的。比如在定時器里面去檢查隊(duì)列。

運(yùn)行結(jié)果：

VIRTIO_BLK_F_SIZE_MAX:0 _is_mmio:1,is_64:0,_is_prefetchable:0 VIRTIO_BLK_F_SEG_MAX:7e addr_size:1000 VIRTIO_BLK cylinders:2,heads:10,sectors:3f addr_64:febd1000 VIRTIO_BLK_F_BLK_SIZE:200 msix_table_bar:1,val:1,off:44 VIRTIO_BLK topology,physical_block_exp:0,alignment:0,min_io_size:0,opt_io_size:0 [0:4.0] vid:id = 1af4:1000 VIRTIO_BLK_F_WCE:1bar[1]: 32bits addr=000000000000C040 size=20 VIRTIO_BLK readonlybar[2]: 32bits addr=00000000FEBD1000 size=1000 [0:3.0] vid:id = 1af4:1001IRQ = 11bar[1]: 32bits addr=000000000000C000 size=40Have MSI-X! bar[2]: 32bits addr=00000000FEBD0000 size=1000msix_location: 64 IRQ = 11msix_ctrl: 2 Have MSI-X! msix_msgnum: 3 msix_location: 64 msix_table_bar: 1 msix_ctrl: 1 msix_table_offset: 0 msix_msgnum: 2 msix_pba_bar: 1 msix_table_bar: 1 msix_pba_offset: 2048msix_table_offset: 0ap start donemsix_pba_bar: 1 msix_pba_offset: 2048 register_irq_handler:100,handler:FFFFFFFF81009120 pci_msix_enable msix_bar:ffffffff810334a0,1 map phy:fea00000 to vaddr:ffffffe8fea00000,&pte:ffffffff80010fa8,pte:fea0009b,511,419,501 ctrl:8001, c001 c001,num:2 msix_mask_entry:0,ffffffe8febd000c,1 msix_mask_entry:1,ffffffe8febd001c,1 msix_mask_entry:0,ffffffe8febd000c,1 msix_write_entry addr:ffffffe8febd0000,msiaddr:fee00000,data:4064 get:fee00000,4064 msix unmask entry :ffffffe8febd000c,1 unmask :0,0,0 free_first:0000000000000000,left:125,dev->threads:0,n:3 vd->addr:10331a0,vd->len:10,vd->flags:1 vd->addr:10331c0,vd->len:200,vd->flags:3 vd->addr:10331b8,vd->len:1,vd->flags:3 cmos:2020-6-5 14:37:3 ****virtio_blk_irq_handler**** irq:100,isr:1 cpu:0 virtio_blk_from_queue:ffffffff810331a0,len:201,status:0,thread:kmain addr:ffffffff810331c0: ~810331c0 - 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................ ~810331d0 - 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................ ~810331e0 - 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................ ~810331f0 - 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................ ~81033200 - 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................ ~81033210 - 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................ ~81033220 - 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................ ~81033230 - 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................ ~81033240 - 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................ ~81033250 - 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................ ~81033260 - 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................ ~81033270 - 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................ ~81033280 - 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................ ~81033290 - 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................ ~810332a0 - 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................ ~810332b0 - 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................ ~810332c0 - 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................ ~810332d0 - 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................ ~810332e0 - 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................ ~810332f0 - 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................ ~81033300 - 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................ ~81033310 - 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................ ~81033320 - 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................ ~81033330 - 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................ ~81033340 - 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................ ~81033350 - 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................ ~81033360 - 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................ ~81033370 - 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................ ~81033380 - 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................ ~81033390 - 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................ ~810333a0 - 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................ ~810333b0 - 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................ free_first:0000000000000003,left:125,dev->threads:0,n:3 vd->addr:10331a0,vd->len:10,vd->flags:1 vd->addr:10331c0,vd->len:200,vd->flags:3 vd->addr:10331b8,vd->len:1,vd->flags:3 ****virtio_blk_irq_handler**** irq:100,isr:1 cpu:0 virtio_blk_from_queue:ffffffff810331a0,len:201,status:0,thread:kmain addr:ffffffff810331c0: ~810331c0 - 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................ ~810331d0 - 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................ ~810331e0 - 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................ ~810331f0 - 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................ ~81033200 - 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................ ~81033210 - 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................ ~81033220 - 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................ ~81033230 - 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................ ~81033240 - 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................ ~81033250 - 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................ ~81033260 - 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................ ~81033270 - 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................ ~81033280 - 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................ ~81033290 - 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................ ~810332a0 - 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................ ~810332b0 - 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................ ~810332c0 - 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................ ~810332d0 - 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................ ~810332e0 - 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................ ~810332f0 - 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................ ~81033300 - 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................ ~81033310 - 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................ ~81033320 - 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................ ~81033330 - 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................ ~81033340 - 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................ ~81033350 - 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................ ~81033360 - 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................ ~81033370 - 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................ ~81033380 - 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................ ~81033390 - 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................ ~810333a0 - 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................ ~810333b0 - 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................ pstatus:ffffffff81022680,name:slub_mm,status:0 ht:ffffffff810139c0,0 task:ffffffff81022580 alloc 4k:2000 create_thread_oncpu:ffffffff810225d0,stack:ffffffff8003b000,name:tasklet 0 cpu:0,flag:1,state:1 switch first to tasklet ffffffff8003cff8,from:kmain cpu:0 new stack:ffffffff8003cff8,old stack:ffffffff81021ef0 pml4base 102e000 102c000 102b000 511 510 0 thread_main:ffffffff810225d0,ffffffff810139c0,tasklet smp_thread_main:ffffffff810139c0 flag:9 KHeap: Free:ffffffff81014000,addr,size:2000

可以看到內(nèi)存打印了2次，內(nèi)容都是0，那是user.img生成的時候，清0了。

QEMUOPTS =-enable-kvm -cpu host,+x2apic -device virtio-blk-pci,id=blk0,drive=hd0,scsi=off -drive file=./usr.img,if=none,id=hd0,cache=none,aio=native-netdev type=tap,script=qemu-ifup.sh,id=net0 -device virtio-net-pci,netdev=net0 -vga vmware -display vnc=192.168.10.2:10-smp 2 -m 512 $(QEMUEXTRA)yaos.img: $(OUT)/bootblock $(OUT)/kernel.elfdd if=/dev/zero of=yaos.img count=10000dd if=$(OUT)/bootblock of=yaos.img conv=notruncdd if=$(OUT)/kernel.elf of=yaos.img seek=1 conv=notruncusr.img: $(OUT)/kernel.elfdd if=/dev/zero of=usr.img count=100qemuimg: yaos.img@echo Ctrl+a h for help$(QEMU) -serial mon:stdio -nographic $(QEMUOPTS) -hda yaos.img qemu: out/kernel.elf user.img@echo Ctrl+a h for help$(QEMU) -serial mon:stdio -nographic $(QEMUOPTS) -kernel out/kernel.elf

QEMUOPTS 做了修改，創(chuàng)建了virtio-blk硬盤，文件為usr.img

運(yùn)行本例：

git clone https://github.com/saneee/x86_64_kernel.git cd 0020 make qemu

總結(jié)

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