[PATCH 02/10] linux: Simplify opendir buffer allocation

[Adhemerval Zanella <adhemerval.zanella@linaro.org>]

THe fallback allocation is removed, so the possible size constraint
should be analized just once; __alloc_dir assumes that 'statp'
argument is non-null, and the max_buffer_size move to close its
used.

Checked on x86_64-linux-gnu and i686-linux-gnu.
---
 include/dirent.h                  |  3 +-
 sysdeps/unix/sysv/linux/opendir.c | 52 +++++++++++--------------------
 2 files changed, 21 insertions(+), 34 deletions(-)

diff --git a/include/dirent.h b/include/dirent.h
index 2b1cdcf8bd..fdf4c4a2f1 100644
--- a/include/dirent.h
+++ b/include/dirent.h
@@ -48,7 +48,8 @@ extern int __versionsort64 (const struct dirent64 **a,
 			    const struct dirent64 **b)
      __attribute_pure__;
 extern DIR *__alloc_dir (int fd, bool close_fd, int flags,
-			 const struct stat64 *statp) attribute_hidden;
+			 const struct stat64 *statp)
+     __nonnull (4) attribute_hidden;
 extern __typeof (rewinddir) __rewinddir;
 extern __typeof (seekdir) __seekdir;
 extern __typeof (dirfd) __dirfd;
diff --git a/sysdeps/unix/sysv/linux/opendir.c b/sysdeps/unix/sysv/linux/opendir.c
index c6ab79246c..765c8104b3 100644
--- a/sysdeps/unix/sysv/linux/opendir.c
+++ b/sysdeps/unix/sysv/linux/opendir.c
@@ -23,12 +23,6 @@
 
 #include <not-cancel.h>
 
-/* The st_blksize value of the directory is used as a hint for the
-   size of the buffer which receives struct dirent values from the
-   kernel.  st_blksize is limited to MAX_DIR_BUFFER_SIZE, in case the
-   file system provides a bogus value.  */
-#define MAX_DIR_BUFFER_SIZE 1048576U
-
 enum {
   opendir_oflags = O_RDONLY|O_NDELAY|O_DIRECTORY|O_LARGEFILE|O_CLOEXEC
 };
@@ -100,38 +94,30 @@ __alloc_dir (int fd, bool close_fd, int flags, const struct stat64 *statp)
      file descriptor.  */
   if (!close_fd
       && __glibc_unlikely (__fcntl64_nocancel (fd, F_SETFD, FD_CLOEXEC) < 0))
-	goto lose;
-
-  const size_t default_allocation = (4 * BUFSIZ < sizeof (struct dirent64)
-				     ? sizeof (struct dirent64) : 4 * BUFSIZ);
-  const size_t small_allocation = (BUFSIZ < sizeof (struct dirent64)
-				   ? sizeof (struct dirent64) : BUFSIZ);
-  size_t allocation = default_allocation;
-#ifdef _STATBUF_ST_BLKSIZE
+    return NULL;
+
+  /* The st_blksize value of the directory is used as a hint for the
+     size of the buffer which receives struct dirent values from the
+     kernel.  st_blksize is limited to max_buffer_size, in case the
+     file system provides a bogus value.  */
+  enum { max_buffer_size = 1U << 20 };
+
+  const size_t allocation_size = 4 * BUFSIZ;
+  _Static_assert (allocation_size >= sizeof (struct dirent64),
+		  "allocation_size < sizeof (struct dirent64)");
+
   /* Increase allocation if requested, but not if the value appears to
-     be bogus.  */
-  if (statp != NULL)
-    allocation = MIN (MAX ((size_t) statp->st_blksize, default_allocation),
-		      MAX_DIR_BUFFER_SIZE);
-#endif
+     be bogus.  It will be between 32Kb (for blocksizes smaller than BUFSIZ)
+     up to 1Mb.  */
+  size_t allocation = MIN (MAX ((size_t) statp->st_blksize, allocation_size),
+			   max_buffer_size);
 
   DIR *dirp = (DIR *) malloc (sizeof (DIR) + allocation);
   if (dirp == NULL)
     {
-      allocation = small_allocation;
-      dirp = (DIR *) malloc (sizeof (DIR) + allocation);
-
-      if (dirp == NULL)
-      lose:
-	{
-	  if (close_fd)
-	    {
-	      int save_errno = errno;
-	      __close_nocancel_nostatus (fd);
-	      __set_errno (save_errno);
-	    }
-	  return NULL;
-	}
+      if (close_fd)
+	__close_nocancel_nostatus (fd);
+      return NULL;
     }
 
   dirp->fd = fd;
-- 
2.17.1