xv6 學習紀錄

課程連結：6.S081 Lecture 17: Virtual Memory for Applications

Lab 連結：Lab: mmap Lab: mmap (hard) The mmap and munmap system calls allow UNIX programs to exert detailed control over their address spaces. They can be used to share memory among processes, to map files into process address spaces, and as part of user-level page fault schemes such as the garbage-collection algorithms discussed in lecture. In this lab you’ll add mmap and munmap to xv6, focusing on memory-mapped files. 目前的理解會像是把 memory address map 到一個 file 中，可以有多個 process share 同一份資料的好處 ...

這一篇筆記主要是為了 lab: network driver 中，要我們先讀一下 xv6 book ch5: Interrupts and device drivers，這篇文章是我自己的筆記 Interrupts and device drivers Driver 需要了解 device 的 interface，可能很複雜或是文件寫得很差 Device 通常可以製造一些 interrupt, 在 xv6 中，這在 devintr() 中處理 kernel/trap.c: devintr(): 像是這裡回傳是否為 device interrupt // check if it's an external interrupt or software interrupt, // and handle it. // returns 2 if timer interrupt, // 1 if other device, // 0 if not recognized. int devintr() { uint64 scause = r_scause(); if((scause & 0x8000000000000000L) && (scause & 0xff) == 9){ // this is a supervisor external interrupt, via PLIC. // irq indicates which device interrupted. int irq = plic_claim(); if(irq == UART0_IRQ){ uartintr(); } else if(irq == VIRTIO0_IRQ){ virtio_disk_intr(); } #ifdef LAB_NET else if(irq == E1000_IRQ){ e1000_intr(); } #endif else if(irq){ printf("unexpected interrupt irq=%d\n", irq); } // the PLIC allows each device to raise at most one // interrupt at a time; tell the PLIC the device is // now allowed to interrupt again. if(irq) plic_complete(irq); return 1; } else if(scause == 0x8000000000000001L){ // software interrupt from a machine-mode timer interrupt, // forwarded by timervec in kernelvec.S. if(cpuid() == 0){ clockintr(); } // acknowledge the software interrupt by clearing // the SSIP bit in sip. w_sip(r_sip() & ~2); return 2; } else { return 0; } } 許多 device driver 分為兩個部份： process’s kernel thread interrupt time 接著分別使用 Console input/output 來看 driver 如何運作 ...

課程連結：6.S081 Fall 2020 Lecture 21: Networking Protocal nesting header 的 type 決定了之後的內容要如何解讀 The OS network stack tcpdump 的解析 Queue 的使用 影片中有提及不管是在那一個層級的 stack 當中，queue 的使用都是很常見的 可能會有一個 buffer allocator MBUF E1000 NIC 這在 lab: network driver 中會運用的一個 NIC, 影片中有提及跟現代的 NIC 比較起來 現在的 NIC 當中有做一些 check Livelock Problem 最後的結論是用 Polling 來解決

Lab 連結：Lab net: Network driver Background You’ll use a network device called the E1000 to handle network communication. To xv6 (and the driver you write), the E1000 looks like a real piece of hardware connected to a real Ethernet local area network (LAN). In fact, the E1000 your driver will talk to is an emulation provided by qemu, connected to a LAN that is also emulated by qemu. On this emulated LAN, xv6 (the “guest”) has an IP address of 10.0.2.15. Qemu also arranges for the computer running qemu to appear on the LAN with IP address 10.0.2.2. When xv6 uses the E1000 to send a packet to 10.0.2.2, qemu delivers the packet to the appropriate application on the (real) computer on which you’re running qemu (the “host”). ...