static int
_pipeisclosed(struct Fd *fd, struct Pipe *p)
{
int res;
uint32_t runs1, runs2;
// Your code here.
//
// Check pageref(fd) and pageref(p),
// returning 1 if they're the same, 0 otherwise.
//
// The logic here is that pageref(p) is the total
// number of readers *and* writers, whereas pageref(fd)
// is the number of file descriptors like fd (readers if fd is
// a reader, writers if fd is a writer).
//
// If the number of file descriptors like fd is equal
// to the total number of readers and writers, then
// everybody left is what fd is. So the other end of
// the pipe is closed.
for (;;) {
runs1 = env->env_runs;
res = pageref(fd) == pageref(p);
runs2 = env->env_runs;
if (runs1 == runs2)
return res;
if ((runs1 != runs2) && res)
cprintf("pipe race avoided\n");
}
}
static int
_pipeisclosed(struct Fd *fd, struct Pipe *p)
{
// Your code here.
//
// Check pageref(fd) and pageref(p),
// returning 1 if they're the same, 0 otherwise.
//
// The logic here is that pageref(p) is the total
// number of readers *and* writers, whereas pageref(fd)
// is the number of file descriptors like fd (readers if fd is
// a reader, writers if fd is a writer).
//
// If the number of file descriptors like fd is equal
// to the total number of readers and writers, then
// everybody left is what fd is. So the other end of
// the pipe is closed.
int runs, r;
do {
runs = env->env_runs;
r = 0;
if (pageref(fd) == pageref(p))
r = 1;
} while (runs != env->env_runs);
return r;
}
static int
_pipeisclosed(struct Fd *fd, struct Pipe *p)
{
// Check pageref(fd) and pageref(p),
// returning 1 if they're the same, 0 otherwise.
//
// The logic here is that pageref(p) is the total
// number of readers *and* writers, whereas pageref(fd)
// is the number of file descriptors like fd (readers if fd is
// a reader, writers if fd is a writer).
//
// If the number of file descriptors like fd is equal
// to the total number of readers and writers, then
// everybody left is what fd is. So the other end of
// the pipe is closed.
//
// LAB 5: Your code here.
while (true) {
uint32_t before = thisenv->env_runs;
bool test = (pageref(fd) == pageref(p));
asm volatile("" : : : "memory");
if (before == thisenv->env_runs) return test;
if (test) cprintf("pipe race avoided\n");
}
}
// Look up an open file for envid.
int
openfile_lookup(envid_t envid, uint32_t fileid, struct OpenFile **po)
{
struct OpenFile *o;
o = &opentab[fileid % MAXOPEN];
if (pageref(o->o_fd) == 1 || o->o_fileid != fileid) {
cprintf("pageref(o->o_fd) is %d\n", pageref(o->o_fd));
return -E_INVAL;
}
*po = o;
return 0;
}
static int
_pipeisclosed(struct Fd *fd, struct Pipe *p)
{
int n, nn, ret;
while (1) {
n = thisenv->env_runs;
ret = pageref(fd) == pageref(p);
nn = thisenv->env_runs;
if (n == nn)
return ret;
if (n != nn && ret == 1)
cprintf("pipe race avoided\n", n, thisenv->env_runs, ret);
}
}
// Allocate an open file.
int
open_alloc(struct Open **o)
{
int i, r;
// Find an available open-file table entry
for (i = 0; i < MAXOPEN; i++) {
switch (pageref(opentab[i].o_ff)) {
case 0:
//writef("^^^^^^^^^^^^^^^^ (u_int)opentab[i].o_ff: %x\n",(u_int)opentab[i].o_ff);
if ((r = syscall_mem_alloc(0, (u_int)opentab[i].o_ff,
PTE_V | PTE_R | PTE_LIBRARY)) < 0) {
return r;
}
case 1:
opentab[i].o_fileid += MAXOPEN;
*o = &opentab[i];
user_bzero((void *)opentab[i].o_ff, BY2PG);
return (*o)->o_fileid;
}
}
return -E_MAX_OPEN;
}
// Look up an open file for envid.
int
openfile_lookup(envid_t envid, uint32_t fileid, struct OpenFile **po)
{
struct OpenFile *o;
o = &opentab[fileid % MAXOPEN];
if (pageref(o->o_fd) <= 1 || o->o_fileid != fileid)
return -E_INVAL;
*po = o;
return 0;
}
// Look up an open file for envid.
int
open_lookup(u_int envid, u_int fileid, struct Open **po)
{
struct Open *o;
o = &opentab[fileid%MAXOPEN];
if (pageref(o->o_ff) == 1 || o->o_fileid != fileid)
return -E_INVAL;
*po = o;
return 0;
}
static int
_pipeisclosed(struct Fd *fd, struct Pipe *p)
{
// Your code here.
//
// Check pageref(fd) and pageref(p),
// returning 1 if they're the same, 0 otherwise.
//
// The logic here is that pageref(p) is the total
// number of readers *and* writers, whereas pageref(fd)
// is the number of file descriptors like fd (readers if fd is
// a reader, writers if fd is a writer).
//
// If the number of file descriptors like fd is equal
// to the total number of readers and writers, then
// everybody left is what fd is. So the other end of
// the pipe is closed.
int runs;
bool isclosed;
tryagain:
runs = env->env_runs;
//critical section
isclosed = (pageref(fd)==pageref(p));
//end of critical section
if(runs != env->env_runs)
{
if(isclosed)
cprintf("pipe race avoided\n");
goto tryagain;
}
if (isclosed)
return 1;
return 0;
}
// Check that fdnum is in range and mapped.
// If it is, set *fd_store to the fd page virtual address.
//
// Returns 0 on success (the page is in range and mapped), < 0 on error.
// Errors are:
// -E_INVAL: fdnum was either not in range or not mapped.
int
fd_lookup(int fdnum, struct Fd **fd_store)
{
struct Fd *fd;
if (fdnum >= 0 && fdnum < MAXFD) {
fd = INDEX2FD(fdnum);
if (pageref(fd) > 0) {
*fd_store = fd;
return 0;
}
}
*fd_store = 0;
return -E_INVAL;
}
// Finds the smallest i from 0 to MAXFD-1 that doesn't have
// its fd page mapped.
// Sets *fd_store to the corresponding fd page virtual address.
//
// fd_alloc does NOT actually allocate an fd page.
// It is up to the caller to allocate the page somehow.
// This means that if someone calls fd_alloc twice in a row
// without allocating the first page we return, we'll return the same
// page the second time.
//
// Hint: Use INDEX2FD.
//
// Returns 0 on success, < 0 on error. Errors are:
// -E_MAX_FD: no more file descriptors
// On error, *fd_store is set to 0.
int
fd_alloc(struct Fd **fd_store)
{
struct Fd *fd;
int i;
for (i = 0; i < MAXFD; i++) {
fd = INDEX2FD(i);
if (pageref(fd) == 0) {
*fd_store = fd;
return 0;
}
}
*fd_store = 0;
return -E_MAX_OPEN;
}
// Close the file descriptor.
//
static int
devfile_close(struct Fd *fd)
{
// If this call will close the last reference to the file descriptor,
// then you must account for the outstanding open file reference
// in the inode.
// But the file descriptor might still be open elsewhere
// (because of fork and dup). Use pageref to check.
//
// LAB 5: Your code here.
//cprintf("%d\n", pageref(fd));
if (pageref(fd) > 1)
return 0;
struct Inode *ino;
int r;
if ((r = inode_open(fd->fd_file.inum, &ino)) < 0)
return r;
ino->i_opencount--;
return inode_close(ino);
}
// Allocate an open file.
int
openfile_alloc(struct OpenFile **o)
{
int i, r;
// Find an available open-file table entry
for (i = 0; i < MAXOPEN; i++) {
switch (pageref(opentab[i].o_fd)) {
case 0:
if ((r = sys_page_alloc(0, opentab[i].o_fd, PTE_P|PTE_U|PTE_W)) < 0)
return r;
/* fall through */
case 1:
opentab[i].o_fileid += MAXOPEN;
*o = &opentab[i];
memset(opentab[i].o_fd, 0, PGSIZE);
return (*o)->o_fileid;
}
}
return -E_MAX_OPEN;
}
// Allocate an open file.
int
open_alloc(struct Open **o)
{
int i, r;
// Find an available open-file table entry
for (i = 0; i < MAXOPEN; i++) {
switch (pageref(opentab[i].o_ff)) {
case 0:
if ((r = sys_mem_alloc(0, (u_int)opentab[i].o_ff, PTE_P|PTE_U|PTE_W)) < 0)
return r;
/* fall through */
case 1:
opentab[i].o_fileid += MAXOPEN;
*o = &opentab[i];
memset((void*)opentab[i].o_ff, 0, BY2PG);
return (*o)->o_fileid;
}
}
return -E_MAX_OPEN;
}
void
umain(void)
{
int p[2], r, pid, i, max;
void *va;
struct Fd *fd;
volatile struct Env *kid;
cprintf("testing for dup race...\n");
if ((r = pipe(p)) < 0)
panic("pipe: %e", r);
max = 200;
if ((r = fork()) < 0)
panic("fork: %e", r);
if (r == 0) {
close(p[1]);
//
// Now the ref count for p[0] will toggle between 2 and 3
// as the parent dups and closes it (there's a close implicit in dup).
//
// The ref count for p[1] is 1.
// Thus the ref count for the underlying pipe structure
// will toggle between 3 and 4.
//
// If a clock interrupt catches close between unmapping
// the pipe structure and unmapping the fd, we'll have
// a ref count for p[0] of 3, a ref count for p[1] of 1,
// and a ref count for the pipe structure of 3, which is
// a no-no.
//
// If a clock interrupt catches dup between mapping the
// fd and mapping the pipe structure, we'll have the same
// ref counts, still a no-no.
//
for (i=0; i<max; i++) {
if(pipeisclosed(p[0])){
cprintf("RACE: pipe appears closed\n");
exit();
}
sys_yield();
}
// do something to be not runnable besides exiting
ipc_recv(0,0,0);
}
pid = r;
cprintf("pid is %d\n", pid);
va = 0;
kid = &envs[ENVX(pid)];
cprintf("kid is %d\n", kid-envs);
dup(p[0], 10);
while (kid->env_status == ENV_RUNNABLE)
dup(p[0], 10);
cprintf("child done with loop\n");
if (pipeisclosed(p[0]))
panic("somehow the other end of p[0] got closed!");
if ((r = fd_lookup(p[0], &fd)) < 0)
panic("cannot look up p[0]: %e", r);
va = fd2data(fd);
if (pageref(va) != 3+1)
cprintf("\nchild detected race\n");
else
cprintf("\nrace didn't happen\n", max);
}