More pread, syscall crud

89ae1d13 · Silas Boyd-Wickizer · 47ab9b8c · 89ae1d13 · 89ae1d13 · 89ae1d13
--- a/ipc.h
+++ b/ipc.h
 struct ipcctl {
-  volatile char done;
+  volatile char done:1;
+  volatile char submitted:1;
+
+  off_t off;
  volatile long result;
 };
--- a/kernlet.c
+++ b/kernlet.c
@@ -59,6 +59,7 @@ sys_kernlet(int fd, size_t count, off_t off)
 {
  struct file *f;
  struct work *w;
+  struct ipcctl *ipc = (struct ipcctl *)myproc()->vmap->kshared;

  if(fd < 0 || fd >= NOFILE || (f=myproc()->ofile[fd]) == 0)
    return -1;
@@ -76,5 +77,7 @@ sys_kernlet(int fd, size_t count, off_t off)
    freework(w);
    return -1;
  }
+  ipc->off = off;
+  ipc->submitted = 1;
  return 0;
 }
--- a/preadtest.cc
+++ b/preadtest.cc
@@ -2,6 +2,7 @@
 #include "stat.h"
 #include "fcntl.h"
 #include "user.h"
+#include "lib.h"
 #include "amd64.h"
 #include "ipc.h"

@@ -24,6 +25,31 @@ kernlet_pread(int fd, size_t count, off_t off)
    die("kernlet");
 }

+static ssize_t
+xpread(int fd, void *buf, size_t count, off_t off)
+{
+  if (ipcctl->submitted) {
+    while (ipcctl->done == 0)
+      nop_pause();
+    if (ipcctl->result == -1)
+      goto slow;
+    if (off < ipcctl->off)
+      goto slow;
+    if (off > ipcctl->off + ipcctl->result)
+      goto slow;
+
+    char *kbuf = (char*) (KSHARED+4096);
+    off_t kbufoff = off - ipcctl->off;
+    size_t kbufcount = MIN(count, ipcctl->result - kbufoff);
+
+    memmove(buf, kbuf+kbufoff, kbufcount);
+    return kbufcount;
+  }
+
+slow:
+  return pread(fd, buf, count, off);
+}
+
 int
 main(int ac, char **av)
 {
@@ -44,7 +70,7 @@ main(int ac, char **av)
    kernlet_pread(fd, PSIZE, k);

    for (i = k; i < k+PSIZE; i+=BSIZE)
-      if (pread(fd, buf, BSIZE, i) != BSIZE)
+      if (xpread(fd, buf, BSIZE, i) != BSIZE)
        die("pread failed");
  }
  t1 = rdtsc();