tar: don't assume O_NONBLOCK is benign on regular files

[chaz/tar] / src / misc.c

diff --git a/src/misc.c b/src/misc.c
index b75f2ab4e419e4f9a928e75b25342630f2ad17ec..3add37188903ff2d0f194b81ec8c8ce8c3ceed8c 100644 (file)
--- a/src/misc.c
+++ b/src/misc.c
@@ -616,6 +616,57 @@ deref_stat (char const *name, struct stat *buf)
   return fstatat (chdir_fd, name, buf, fstatat_flags);
 }
 
+/* Read from FD into the buffer BUF with COUNT bytes.  Attempt to fill
+   BUF.  Wait until input is available; this matters because files are
+   opened O_NONBLOCK for security reasons, and on some file systems
+   this can cause read to fail with errno == EAGAIN.  Return the
+   actual number of bytes read, zero for EOF, or
+   SAFE_READ_ERROR upon error.  */
+size_t
+blocking_read (int fd, void *buf, size_t count)
+{
+  size_t bytes = safe_read (fd, buf, count);
+
+#if defined F_SETFL && O_NONBLOCK
+  if (bytes == SAFE_READ_ERROR && errno == EAGAIN)
+    {
+      int flags = fcntl (fd, F_GETFL);
+      if (0 <= flags && flags & O_NONBLOCK
+         && fcntl (fd, F_SETFL, flags & ~O_NONBLOCK) != -1)
+       bytes = safe_read (fd, buf, count);
+    }
+#endif
+
+  return bytes;
+}
+
+/* Write to FD from the buffer BUF with COUNT bytes.  Do a full write.
+   Wait until an output buffer is available; this matters because
+   files are opened O_NONBLOCK for security reasons, and on some file
+   systems this can cause write to fail with errno == EAGAIN.  Return
+   the actual number of bytes written, setting errno if that is less
+   than COUNT.  */
+size_t
+blocking_write (int fd, void const *buf, size_t count)
+{
+  size_t bytes = full_write (fd, buf, count);
+
+#if defined F_SETFL && O_NONBLOCK
+  if (bytes < count && errno == EAGAIN)
+    {
+      int flags = fcntl (fd, F_GETFL);
+      if (0 <= flags && flags & O_NONBLOCK
+         && fcntl (fd, F_SETFL, flags & ~O_NONBLOCK) != -1)
+       {
+         char const *buffer = buf;
+         bytes += full_write (fd, buffer + bytes, count - bytes);
+       }
+    }
+#endif
+
+  return bytes;
+}
+
 /* Set FD's (i.e., assuming the working directory is PARENTFD, FILE's)
    access time to ATIME.  */
 int