62 lines
1010 B
C
62 lines
1010 B
C
/*
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* Global memory area system.
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*
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* Works with two system calls:
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*
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* byte = rdglob(addr);
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* success = wrglob(addr,byte);
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*/
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#include "param.h"
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#include "systm.h"
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#include "user.h"
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#ifndef GLOBSZ
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#define GLOBSZ 256
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#endif
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unsigned char global_segment[GLOBSZ];
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void rdglob()
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{
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struct a {
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int addr;
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} *uap = (struct a *)u.u_arg;
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// Only root should have access to the shared memory block
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if(u.u_uid!=0)
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{
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u.u_rval = -1;
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return;
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}
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if(uap->addr>=GLOBSZ)
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{
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u.u_rval = -1;
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return;
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}
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u.u_rval = global_segment[uap->addr];
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}
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void wrglob()
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{
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struct a {
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int addr;
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unsigned char value;
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} *uap = (struct a *)u.u_arg;
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// Only root should have access to the shared memory block
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if(u.u_uid!=0)
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{
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u.u_rval = -1;
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return;
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}
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if(uap->addr>=GLOBSZ)
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{
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u.u_rval = -1;
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return;
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}
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u.u_rval = 0;
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global_segment[uap->addr] = uap->value;
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}
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