Lab: system calls

From: https://pdos.csail.mit.edu/6.S081/2020/labs/syscall.html

【NOTE】Add a new system call

To add a new system call, say, named xxx:

add a prototype for the system call to user/user.h

int xxx(int)

add a stub to user/usys.pl

entry("xxx");

add a syscall number to kernel/syscall.h

#define SYS_xxx 22

add the new syscall into kernel/syscall.c

extern uint64 sys_xxx(void); // 1static uint64 (*syscalls[])(void) = { ... [SYS_xxx] sys_xxx, // 2 };

add sys_xxx (a function takes void as argument and returns uint64) inkernel/sysproc.c. This function do fetch arguments about the system call and return values.

uint64 sys_xxx(void) {// about arguments: the [xv6 book](https://pdos.csail.mit.edu/6.S081/2020/xv6/book-riscv-rev1.pdf) Sections 4.3 and 4.4 of Chapter 4 }

implement the syscall somewhere in the kernel. (e.g. implement a xxx function , defines in kernel/defs.h, to do hard work)

System call tracing

In this assignment you will add a system call tracing feature that may help you when debugging later labs. You’ll create a new trace system call that will control tracing. It should take one argument, an integer “mask”, whose bits specify which system calls to trace. For example, to trace the fork system call, a program calls trace(1 << SYS_fork), where SYS_fork is a syscall number from kernel/syscall.h. You have to modify the xv6 kernel to print out a line when each system call is about to return, if the system call’s number is set in the mask. The line should contain the process id, the name of the system call and the return value; you don’t need to print the system call arguments. The tracesystem call should enable tracing for the process that calls it and any children that it subsequently forks, but should not affect other processes.

Main implement

kernel/sysproc.c:

...// * uint64 sys_trace(void) {if (argint(0, &myproc()->tracemask) < 0)return -1;return 0; }

kernel/proc.h:

struct proc {struct spinlock lock;...int pid; // Process ID...int tracemask; // trace mask // * };

kernel/syscall.c:

...extern uint64 sys_chdir(void); extern uint64 sys_close(void); ... extern uint64 sys_trace(void); // *static uint64 (*syscalls[])(void) = { [SYS_fork] sys_fork, [SYS_exit] sys_exit, ... [SYS_trace] sys_trace, // * };char *syscallnames[] = { [SYS_fork] "fork", [SYS_exit] "exit", ... [SYS_trace] "trace", // * };void syscall(void) {...// trace // *if (p->tracemask >> num) {printf("%d: syscall %s -> %d\n", p->pid, syscallnames[num], p->trapframe->a0);} }

Detailed diff

diff --git a/Makefile b/Makefile index f0beb51..1c07efd 100644 --- a/Makefile +++ b/Makefile @@ -149,6 +149,7 @@ UPROGS=\$U/_grind\$U/_wc\$U/_zombie\ + $U/_trace\diff --git a/gradelib.pyc b/gradelib.pyc new file mode 100644 index 0000000..d118849 Binary files /dev/null and b/gradelib.pyc differ diff --git a/kernel/proc.c b/kernel/proc.c index 6afafa1..73845e4 100644 --- a/kernel/proc.c +++ b/kernel/proc.c @@ -280,6 +280,9 @@ fork(void)// copy saved user registers.*(np->trapframe) = *(p->trapframe);+ // copy trace mask + np->tracemask = p->tracemask; +// Cause fork to return 0 in the child.np->trapframe->a0 = 0;diff --git a/kernel/proc.h b/kernel/proc.h index 9c16ea7..cf18b9b 100644 --- a/kernel/proc.h +++ b/kernel/proc.h @@ -103,4 +103,6 @@ struct proc {struct file *ofile[NOFILE]; // Open filesstruct inode *cwd; // Current directorychar name[16]; // Process name (debugging) + + int tracemask; // trace mask}; diff --git a/kernel/syscall.c b/kernel/syscall.c index c1b3670..182ca99 100644 --- a/kernel/syscall.c +++ b/kernel/syscall.c @@ -104,6 +104,7 @@ extern uint64 sys_unlink(void);extern uint64 sys_wait(void);extern uint64 sys_write(void);extern uint64 sys_uptime(void); +extern uint64 sys_trace(void);static uint64 (*syscalls[])(void) = {[SYS_fork] sys_fork, @@ -127,6 +128,32 @@ static uint64 (*syscalls[])(void) = {[SYS_link] sys_link,[SYS_mkdir] sys_mkdir,[SYS_close] sys_close, +[SYS_trace] sys_trace, +}; + +char *syscallnames[] = { +[SYS_fork] "fork", +[SYS_exit] "exit", +[SYS_wait] "wait", +[SYS_pipe] "pipe", +[SYS_read] "read", +[SYS_kill] "kill", +[SYS_exec] "exec", +[SYS_fstat] "fstat", +[SYS_chdir] "chdir", +[SYS_dup] "dup", +[SYS_getpid] "getpid", +[SYS_sbrk] "sbrk", +[SYS_sleep] "sleep", +[SYS_uptime] "uptime", +[SYS_open] "open", +[SYS_write] "write", +[SYS_mknod] "mknod", +[SYS_unlink] "unlink", +[SYS_link] "link", +[SYS_mkdir] "mkdir", +[SYS_close] "close", +[SYS_trace] "trace",};void @@ -143,4 +170,10 @@ syscall(void)p->pid, p->name, num);p->trapframe->a0 = -1;} + + // trace + if (p->tracemask >> num) { + printf("%d: syscall %s -> %d\n", + p->pid, syscallnames[num], p->trapframe->a0); + }} diff --git a/kernel/syscall.h b/kernel/syscall.h index bc5f356..01004db 100644 --- a/kernel/syscall.h +++ b/kernel/syscall.h @@ -20,3 +20,5 @@#define SYS_link 19#define SYS_mkdir 20#define SYS_close 21 + +#define SYS_trace 22 diff --git a/kernel/sysproc.c b/kernel/sysproc.c index e8bcda9..7a078c0 100644 --- a/kernel/sysproc.c +++ b/kernel/sysproc.c @@ -95,3 +95,12 @@ sys_uptime(void)release(&tickslock);return xticks;} + +uint64 +sys_trace(void) +{ + if (argint(0, &myproc()->tracemask) < 0) + return -1; + + return 0; +} diff --git a/user/user.h b/user/user.h index b71ecda..774bb03 100644 --- a/user/user.h +++ b/user/user.h @@ -24,6 +24,8 @@ char* sbrk(int);int sleep(int);int uptime(void);+int trace(int); +// ulib.cint stat(const char*, struct stat*);char* strcpy(char*, const char*); diff --git a/user/usys.pl b/user/usys.pl index 01e426e..2e51985 100755 --- a/user/usys.pl +++ b/user/usys.pl @@ -36,3 +36,5 @@ entry("getpid");entry("sbrk");entry("sleep");entry("uptime"); + +entry("trace");

Sysinfo

In this assignment you will add a system call, sysinfo, that collects information about the running system. The system call takes one argument: a pointer to a struct sysinfo (see kernel/sysinfo.h). The kernel should fill out the fields of this struct: the freemem field should be set to the number of bytes of free memory, and the nproc field should be set to the number of processes whose state is not UNUSED. We provide a test program sysinfotest; you pass this assignment if it prints “sysinfotest: OK”.

Main implement

kernel/sysproc.c:

uint64 sys_sysinfo(void) {uint64 info; // user pointer to struct statif(argaddr(0, &info) < 0)return -1;return systeminfo(info); }

kernel/sysinfo.c:

#include "types.h" #include "riscv.h" #include "param.h" #include "spinlock.h" #include "defs.h" #include "sysinfo.h" #include "proc.h"// Get current system info // addr is a user virtual address, pointing to a struct sysinfo. int systeminfo(uint64 addr) {struct proc *p = myproc();struct sysinfo info;info.freemem = freemem();info.nproc = nproc();if(copyout(p->pagetable, addr, (char *)&info, sizeof(info)) < 0)return -1;return 0; }

kernel/proc.c:

// Get the number of processes whose state is not UNUSED. int nproc(void) {int n = 0;struct proc *p;for(p = proc; p < &proc[NPROC]; p++) {acquire(&p->lock);if(p->state != UNUSED)++n;release(&p->lock);}return n; }

kernel/kalloc.c:

// Get the number of bytes of free memory int freemem(void) {int n = 0;struct run *r;acquire(&kmem.lock);for (r = kmem.freelist; r; r = r->next)++n;release(&kmem.lock);return n * 4096; }

Detailed diff

diff --git a/Makefile b/Makefile index 1c07efd..b626677 100644 --- a/Makefile +++ b/Makefile @@ -36,6 +36,7 @@ OBJS = \$K/kernelvec.o \$K/plic.o \$K/virtio_disk.o \ + $K/sysinfo.o \ifeq ($(LAB),pgtbl)OBJS += $K/vmcopyin.o @@ -150,6 +151,7 @@ UPROGS=\$U/_wc\$U/_zombie\$U/_trace\ + $U/_sysinfotest\diff --git a/kernel/defs.h b/kernel/defs.h index 4b9bbc0..7ebebb8 100644 --- a/kernel/defs.h +++ b/kernel/defs.h @@ -8,6 +8,7 @@ struct spinlock;struct sleeplock;struct stat;struct superblock; +struct sysinfo;// bio.cvoid binit(void); @@ -63,6 +64,7 @@ void ramdiskrw(struct buf*);void* kalloc(void);void kfree(void *);void kinit(void); +int freemem(void);// log.cvoid initlog(int, struct superblock*); @@ -104,6 +106,7 @@ void yield(void);int either_copyout(int user_dst, uint64 dst, void *src, uint64 len);int either_copyin(void *dst, int user_src, uint64 src, uint64 len);void procdump(void); +int nproc(void);// swtch.Svoid swtch(struct context*, struct context*); @@ -183,5 +186,8 @@ void virtio_disk_init(void);void virtio_disk_rw(struct buf *, int);void virtio_disk_intr(void);+// sysinfo.c +int systeminfo(uint64); +// number of elements in fixed-size array#define NELEM(x) (sizeof(x)/sizeof((x)[0])) diff --git a/kernel/kalloc.c b/kernel/kalloc.c index fa6a0ac..5051a1d 100644 --- a/kernel/kalloc.c +++ b/kernel/kalloc.c @@ -80,3 +80,19 @@ kalloc(void)memset((char*)r, 5, PGSIZE); // fill with junkreturn (void*)r;} + +// Get the number of bytes of free memory +int +freemem(void) +{ + int n = 0; + struct run *r; + acquire(&kmem.lock); + + for (r = kmem.freelist; r; r = r->next) + ++n; + + release(&kmem.lock); + + return n * 4096; +} diff --git a/kernel/proc.c b/kernel/proc.c index 73845e4..73d2745 100644 --- a/kernel/proc.c +++ b/kernel/proc.c @@ -696,3 +696,20 @@ procdump(void)printf("\n");}} + +// Get the number of processes whose state is not UNUSED. +int +nproc(void) +{ + int n = 0; + struct proc *p; + + for(p = proc; p < &proc[NPROC]; p++) { + acquire(&p->lock); + if(p->state != UNUSED) + ++n; + release(&p->lock); + } + + return n; +} diff --git a/kernel/syscall.c b/kernel/syscall.c index 182ca99..fdf996d 100644 --- a/kernel/syscall.c +++ b/kernel/syscall.c @@ -105,6 +105,7 @@ extern uint64 sys_wait(void);extern uint64 sys_write(void);extern uint64 sys_uptime(void);extern uint64 sys_trace(void); +extern uint64 sys_sysinfo(void);static uint64 (*syscalls[])(void) = {[SYS_fork] sys_fork, @@ -129,6 +130,7 @@ static uint64 (*syscalls[])(void) = {[SYS_mkdir] sys_mkdir,[SYS_close] sys_close,[SYS_trace] sys_trace, +[SYS_sysinfo] sys_sysinfo,};char *syscallnames[] = { @@ -154,6 +156,7 @@ char *syscallnames[] = {[SYS_mkdir] "mkdir",[SYS_close] "close",[SYS_trace] "trace", +[SYS_sysinfo] "sysinfo",};void diff --git a/kernel/syscall.h b/kernel/syscall.h index 01004db..6716e88 100644 --- a/kernel/syscall.h +++ b/kernel/syscall.h @@ -22,3 +22,4 @@#define SYS_close 21#define SYS_trace 22 +#define SYS_sysinfo 23 diff --git a/kernel/sysinfo.c b/kernel/sysinfo.c new file mode 100644 index 0000000..40bd08a --- /dev/null +++ b/kernel/sysinfo.c @@ -0,0 +1,22 @@ +#include "types.h" +#include "riscv.h" +#include "param.h" +#include "spinlock.h" +#include "defs.h" +#include "sysinfo.h" +#include "proc.h" + +// Get current system info +// addr is a user virtual address, pointing to a struct sysinfo. +int +systeminfo(uint64 addr) { + struct proc *p = myproc(); + struct sysinfo info; + + info.freemem = freemem(); + info.nproc = nproc(); + + if(copyout(p->pagetable, addr, (char *)&info, sizeof(info)) < 0) + return -1; + return 0; +} diff --git a/kernel/sysproc.c b/kernel/sysproc.c index 7a078c0..a1231d0 100644 --- a/kernel/sysproc.c +++ b/kernel/sysproc.c @@ -104,3 +104,13 @@ sys_trace(void)return 0;} + +uint64 +sys_sysinfo(void) +{ + uint64 info; // user pointer to struct stat + + if(argaddr(0, &info) < 0) + return -1; + return systeminfo(info); +} diff --git a/time.txt b/time.txt new file mode 100644 index 0000000..0cfbf08 --- /dev/null +++ b/time.txt @@ -0,0 +1 @@ +2 diff --git a/user/user.h b/user/user.h index 774bb03..708496d 100644 --- a/user/user.h +++ b/user/user.h @@ -1,5 +1,6 @@struct stat;struct rtcdate; +struct sysinfo;// system callsint fork(void); @@ -25,6 +26,7 @@ int sleep(int);int uptime(void);int trace(int); +int sysinfo(struct sysinfo *);// ulib.cint stat(const char*, struct stat*); diff --git a/user/usys.pl b/user/usys.pl index 2e51985..fce5771 100755 --- a/user/usys.pl +++ b/user/usys.pl @@ -38,3 +38,4 @@ entry("sleep");entry("uptime");entry("trace"); +entry("sysinfo");

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EOF

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By CDFMLR 2020-03-02

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