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https://github.com/SmallPond/MIT6.828_OS.git
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91 lines
2.4 KiB
C
91 lines
2.4 KiB
C
// Ping-pong a counter between two processes.
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// Only need to start one of these -- splits into two, crudely.
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#include <inc/string.h>
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#include <inc/lib.h>
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envid_t dumbfork(void);
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void
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umain(int argc, char **argv)
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{
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envid_t who;
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int i;
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// fork a child process
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who = dumbfork();
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// print a message and yield to the other a few times
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for (i = 0; i < (who ? 10 : 20); i++) {
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cprintf("%d: I am the %s!\n", i, who ? "parent" : "child");
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sys_yield();
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}
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}
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void
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duppage(envid_t dstenv, void *addr)
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{
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int r;
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// This is NOT what you should do in your fork.
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if ((r = sys_page_alloc(dstenv, addr, PTE_P|PTE_U|PTE_W)) < 0)
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panic("sys_page_alloc: %e", r);
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// dstenv 的 addr 映射到 envs[0]的UTEMP，
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if ((r = sys_page_map(dstenv, addr, 0, UTEMP, PTE_P|PTE_U|PTE_W)) < 0)
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panic("sys_page_map: %e", r);
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memmove(UTEMP, addr, PGSIZE);
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if ((r = sys_page_unmap(0, UTEMP)) < 0)
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panic("sys_page_unmap: %e", r);
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}
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envid_t
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dumbfork(void)
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{
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envid_t envid;
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uint8_t *addr;
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int r;
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extern unsigned char end[];
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// Allocate a new child environment.
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// The kernel will initialize it with a copy of our register state,
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// so that the child will appear to have called sys_exofork() too -
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// except that in the child, this "fake" call to sys_exofork()
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// will return 0 instead of the envid of the child.
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envid = sys_exofork();
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cprintf("envid: %d\n",envid);
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if (envid < 0)
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panic("sys_exofork: %e", envid);
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if (envid == 0) {
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// We're the child.
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// The copied value of the global variable 'thisenv'
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// is no longer valid (it refers to the parent!).
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// Fix it and return 0.
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// "child, sysgetenvid() : 1
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// cprintf("child, sysgetenvid() :%d\n", ENVX(sys_getenvid()));
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thisenv = &envs[ENVX(sys_getenvid())];
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return 0;
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}
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// We're the parent.
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// Eagerly copy our entire address space into the child.
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// This is NOT what you should do in your fork implementation.
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// 用户程序通常从 UTEXT处开始。
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for (addr = (uint8_t*) UTEXT; addr < end; addr += PGSIZE) {
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// copying addr :00800000
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// copying addr :00801000
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// copying addr :00802000
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cprintf("copying addr :%08x\n", (uint32_t)addr);
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duppage(envid, addr);
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}
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// Also copy the stack we are currently running on.
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duppage(envid, ROUNDDOWN(&addr, PGSIZE));
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// Start the child environment running
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if ((r = sys_env_set_status(envid, ENV_RUNNABLE)) < 0)
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panic("sys_env_set_status: %e", r);
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return envid;
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}
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