lib/ipc.c

   1 // User-level IPC library routines
   2
   3 #include <inc/lib.h>
   4 // Receive a value via IPC and return it.
   5 // If 'pg' is nonnull, then any page sent by the sender will be mapped at
   6 //      that address.
   7 // If 'fromenv' is nonnull, then store the IPC sender's envid in *fromenv.
   8 // If 'perm' is nonnull, then store the IPC sender's page permission in *perm
   9 //      (this is nonzero iff a page was successfully transferred to 'pg').
  10 // If the system call fails, then store 0 in *fromenv and *perm (if
  11 //      they're nonnull) and return the error.
  12 //
  13 // Hint:
  14 //   Use 'env' to discover the value and who sent it.
  15 //   If 'pg' is null, pass sys_ipc_recv a value that it will understand
  16 //   as meaning "no page".  (Zero is not the right value.)
  17 int32_t
  18 ipc_recv(envid_t *from_env_store, void *pg, int *perm_store)
  19 {
  20         // LAB 4: Your code here.
  21         int r;
  22
  23         if (!pg)
  24                 pg = (void *)USTACKTOP;
  25
  26         if ((r = sys_ipc_recv(pg)) < 0) {
  27                 if (from_env_store)
  28                         *from_env_store = 0;
  29                 if (perm_store)
  30                         *perm_store = 0;
  31                 return r;
  32         } else {
  33                 if (from_env_store)
  34                         *from_env_store = env->env_ipc_from;
  35                 if (perm_store)
  36                         *perm_store = env->env_ipc_perm;
  37                 return env->env_ipc_value;
  38         }
  39 }
  40
  41 // Send 'val' (and 'pg' with 'perm', assuming 'pg' is nonnull) to 'toenv'.
  42 // This function keeps trying until it succeeds.
  43 // It should panic() on any error other than -E_IPC_NOT_RECV.
  44 //
  45 // Hint:
  46 //   Use sys_yield() to be CPU-friendly.
  47 //   If 'pg' is null, pass sys_ipc_recv a value that it will understand
  48 //   as meaning "no page".  (Zero is not the right value.)
  49 void
  50 ipc_send(envid_t to_env, uint32_t val, void *pg, int perm)
  51 {
  52         // LAB 4: Your code here.
  53         int r;
  54
  55         while (1) {
  56                 r = sys_ipc_try_send(to_env, val, pg, perm);
  57                 if (r >= 0)
  58                         return;
  59                 if (r != -E_IPC_NOT_RECV)
  60                         panic("sys_ipc_try_send error: %e", r);
  61
  62                 sys_yield();
  63         }
  64 }
  65