First pass at pwrite

08d9fdca · Silas Boyd-Wickizer · d0e7f560 · 08d9fdca · 08d9fdca · 08d9fdca
--- a/include/file.hh
+++ b/include/file.hh
@@ -16,6 +16,7 @@ struct file : public referenced, public rcu_freed {
  int          stat(struct stat*);
  int          read(char *addr, int n);
  ssize_t      pread(char *addr, size_t n, off_t offset);
+  ssize_t      pwrite(const char *addr, size_t n, off_t offset);
  int          write(const char *addr, int n);

  enum { FD_NONE, FD_PIPE, FD_INODE, FD_SOCKET } type;  

--- a/kernel/file.cc
+++ b/kernel/file.cc
@@ -121,3 +121,18 @@ file::write(const char *addr, int n)
    return netwrite(socket, addr, n);
  panic("filewrite");
 }
+
+ssize_t
+file::pwrite(const char *addr, size_t n, off_t off)
+{
+  if(type == file::FD_INODE){
+    int r;
+    ilock(ip, 1);
+    if(ip->type == 0 || ip->type == T_DIR)
+      panic("filewrite but 0 or T_DIR");
+    r = writei(ip, addr, off, n);
+    iunlock(ip);
+    return r;
+  }
+  return -1;
+}
--- a/kernel/sysfile.cc
+++ b/kernel/sysfile.cc
@@ -97,6 +97,33 @@ sys_write(int fd, const void *p, size_t n)
 }

 //SYSCALL
+ssize_t
+sys_pwrite(int fd, const void *ubuf, size_t count, off_t offset)
+{
+  sref<file> f;
+  if (!getfile(fd, &f))
+    return -1;
+
+  if (count < PGSIZE) {
+    ssize_t r;
+    char* b;
+    b = kalloc("pwritebuf");
+    fetchmem(b, ubuf, count);
+    r = f->pwrite(b, count, offset);
+    kfree(b);
+    return r;
+  } else {
+    // XXX(sbw) pagefaulting doesn't guarantee ubuf is mapped 
+    // while pread executes
+    uptr i = (uptr)ubuf;
+    for(uptr va = PGROUNDDOWN(i); va < i+count; va = va + PGSIZE)
+      if(pagefault(myproc()->vmap, va, 0) < 0)
+        return -1;
+    return f->pwrite((char*)ubuf, count, offset);
+  }
+}
+
+//SYSCALL
 int
 sys_close(int fd)
 {