[PATCH 09/10] linux: Use getdents64 on readdir64 compat implementation

[Adhemerval Zanella via Libc-alpha <libc-alpha@sourceware.org>]

It uses a similar strategy from the non-LFS readdir that also
uses getdents64 internally and reserves some space on the allocated
internal DIR buffer to be used as a temporary buffer. The kernel
obtained dirent64 data are copied to the temporary buffer for each
readdir compat call.

It allows to remove __old_getdents64.

Checked on i686-linux-gnu.
---
 sysdeps/unix/sysv/linux/getdents64.c | 95 +---------------------------
 sysdeps/unix/sysv/linux/olddirent.h  |  2 -
 sysdeps/unix/sysv/linux/readdir.h    | 47 +++++++++++++-
 sysdeps/unix/sysv/linux/readdir64.c  | 27 ++++----
 4 files changed, 58 insertions(+), 113 deletions(-)

diff --git a/sysdeps/unix/sysv/linux/getdents64.c b/sysdeps/unix/sysv/linux/getdents64.c
index 75892c2823..f40dfacbfe 100644
--- a/sysdeps/unix/sysv/linux/getdents64.c
+++ b/sysdeps/unix/sysv/linux/getdents64.c
@@ -36,97 +36,4 @@ weak_alias (__getdents64, getdents64)
 
 #if _DIRENT_MATCHES_DIRENT64
 strong_alias (__getdents64, __getdents)
-#else
-# include <shlib-compat.h>
-
-# if SHLIB_COMPAT(libc, GLIBC_2_1, GLIBC_2_2)
-#  include <olddirent.h>
-#  include <unistd.h>
-
-static ssize_t
-handle_overflow (int fd, __off64_t offset, ssize_t count)
-{
-  /* If this is the first entry in the buffer, we can report the
-     error.  */
-  if (offset == 0)
-    {
-      __set_errno (EOVERFLOW);
-      return -1;
-    }
-
-  /* Otherwise, seek to the overflowing entry, so that the next call
-     will report the error, and return the data read so far.  */
-  if (__lseek64 (fd, offset, SEEK_SET) != 0)
-    return -1;
-  return count;
-}
-
-ssize_t
-__old_getdents64 (int fd, char *buf, size_t nbytes)
-{
-  /* We do not move the individual directory entries.  This is only
-     possible if the target type (struct __old_dirent64) is smaller
-     than the source type.  */
-  _Static_assert (offsetof (struct __old_dirent64, d_name)
-		  <= offsetof (struct dirent64, d_name),
-		  "__old_dirent64 is larger than dirent64");
-  _Static_assert (__alignof__ (struct __old_dirent64)
-		  <= __alignof__ (struct dirent64),
-		  "alignment of __old_dirent64 is larger than dirent64");
-
-  ssize_t retval = INLINE_SYSCALL_CALL (getdents64, fd, buf, nbytes);
-  if (retval > 0)
-    {
-      /* This is the marker for the first entry.  Offset 0 is reserved
-	 for the first entry (see rewinddir).  Here, we use it as a
-	 marker for the first entry in the buffer.  We never actually
-	 seek to offset 0 because handle_overflow reports the error
-	 directly, so it does not matter that the offset is incorrect
-	 if entries have been read from the descriptor before (so that
-	 the descriptor is not actually at offset 0).  */
-      __off64_t previous_offset = 0;
-
-      char *p = buf;
-      char *end = buf + retval;
-      while (p < end)
-	{
-	  struct dirent64 *source = (struct dirent64 *) p;
-
-	  /* Copy out the fixed-size data.  */
-	  __ino_t ino = source->d_ino;
-	  __off64_t offset = source->d_off;
-	  unsigned int reclen = source->d_reclen;
-	  unsigned char type = source->d_type;
-
-	  /* Check for ino_t overflow.  */
-	  if (__glibc_unlikely (ino != source->d_ino))
-	    return handle_overflow (fd, previous_offset, p - buf);
-
-	  /* Convert to the target layout.  Use a separate struct and
-	     memcpy to side-step aliasing issues.  */
-	  struct __old_dirent64 result;
-	  result.d_ino = ino;
-	  result.d_off = offset;
-	  result.d_reclen = reclen;
-	  result.d_type = type;
-
-	  /* Write the fixed-sized part of the result to the
-	     buffer.  */
-	  size_t result_name_offset = offsetof (struct __old_dirent64, d_name);
-	  memcpy (p, &result, result_name_offset);
-
-	  /* Adjust the position of the name if necessary.  Copy
-	     everything until the end of the record, including the
-	     terminating NUL byte.  */
-	  if (result_name_offset != offsetof (struct dirent64, d_name))
-	    memmove (p + result_name_offset, source->d_name,
-		     reclen - offsetof (struct dirent64, d_name));
-
-	  p += reclen;
-	  previous_offset = offset;
-	}
-     }
-  return retval;
-}
-# endif /* SHLIB_COMPAT(libc, GLIBC_2_1, GLIBC_2_2)  */
-#endif /* _DIRENT_MATCHES_DIRENT64  */
+#endif
diff --git a/sysdeps/unix/sysv/linux/olddirent.h b/sysdeps/unix/sysv/linux/olddirent.h
index b118b0ef96..63d8e97868 100644
--- a/sysdeps/unix/sysv/linux/olddirent.h
+++ b/sysdeps/unix/sysv/linux/olddirent.h
@@ -36,8 +36,6 @@ extern struct __old_dirent64 *__old_readdir64_unlocked (DIR *__dirp)
         attribute_hidden;
 extern int __old_readdir64_r (DIR *__dirp, struct __old_dirent64 *__entry,
 			  struct __old_dirent64 **__result);
-extern __ssize_t __old_getdents64 (int __fd, char *__buf, size_t __nbytes)
-	attribute_hidden;
 int __old_scandir64 (const char * __dir,
 		     struct __old_dirent64 *** __namelist,
 		     int (*__selector) (const struct __old_dirent64 *),
diff --git a/sysdeps/unix/sysv/linux/readdir.h b/sysdeps/unix/sysv/linux/readdir.h
index 7f6cf3783d..234a7f26e6 100644
--- a/sysdeps/unix/sysv/linux/readdir.h
+++ b/sysdeps/unix/sysv/linux/readdir.h
@@ -21,6 +21,7 @@
 
 #if !_DIRENT_MATCHES_DIRENT64
 # include <dirstream.h>
+# include <olddirent.h>
 
 /* getdents64 is used internally for both LFS and non-LFS implementations.
    The non-LFS interface reserves part of the allocated buffer to return the
@@ -106,9 +107,53 @@ dirstream_ret_entry (struct __dirstream *ds)
 
   return dp;
 }
+
+/* Return the allocated buffer used on LFS compat readdir call.  */
+static inline struct __old_dirent64 *
+dirstream_ret64_compat (struct __dirstream *ds)
+{
+  return (struct __old_dirent64 *) ds->data;
+}
+
+static inline struct __old_dirent64 *
+dirstream_ret_entry64_compat (struct __dirstream *ds)
+{
+  struct dirent64 *dp64 = dirstream_entry (ds);
+  struct __old_dirent64 *dp64_compat = dirstream_ret64_compat (ds);
+
+  dp64_compat->d_ino = dp64->d_ino;
+  if (dp64_compat->d_ino != dp64->d_ino)
+    /* Overflow.  */
+    return NULL;
+
+  dp64_compat->d_off = dp64->d_off;
+
+  const size_t size_diff = (offsetof (struct dirent64, d_name)
+			    - offsetof (struct __old_dirent64, d_name));
+  const size_t alignment = _Alignof (struct __old_dirent64);
+  size_t new_reclen  = (dp64->d_reclen - size_diff + alignment - 1)
+			& ~(alignment - 1);
+  if (new_reclen > return_buffer_size)
+    /* Overflow.  */
+    return NULL;
+
+  /* The compat symbol report the kernel obtained d_reclen, even though
+     it has an incompatible dirent layout.  */
+  dp64_compat->d_reclen = dp64->d_reclen;
+
+  dp64_compat->d_type = dp64->d_type;
+
+  memcpy (dp64_compat->d_name, dp64->d_name,
+	  dp64->d_reclen - offsetof (struct dirent64, d_name));
+
+  ds->offset += dp64->d_reclen;
+  ds->filepos = dp64->d_off;
+
+  return dp64_compat;
+}
+
 #else
 /* No need to reserve an buffer space if dirent has already LFS support.  */
 enum { return_buffer_size = 0 };
 #endif /* _DIRENT_MATCHES_DIRENT64  */
-
 #endif
diff --git a/sysdeps/unix/sysv/linux/readdir64.c b/sysdeps/unix/sysv/linux/readdir64.c
index 4ce6024b38..4095b94a0f 100644
--- a/sysdeps/unix/sysv/linux/readdir64.c
+++ b/sysdeps/unix/sysv/linux/readdir64.c
@@ -108,27 +108,23 @@ weak_alias (__readdir64, readdir)
 # include <shlib-compat.h>
 versioned_symbol (libc, __readdir64, readdir64, GLIBC_2_2);
 # if SHLIB_COMPAT(libc, GLIBC_2_1, GLIBC_2_2)
-#  include <olddirent.h>
+#  include <readdir.h>
+#  include <unistd.h>
 
 attribute_compat_text_section
 struct __old_dirent64 *
 __old_readdir64_unlocked (DIR *dirp)
 {
   struct __old_dirent64 *dp;
-  int saved_errno = errno;
+  const int saved_errno = errno;
 
   do
     {
-      size_t reclen;
-
       if (dirp->offset >= dirp->size)
 	{
 	  /* We've emptied out our buffer.  Refill it.  */
-
-	  size_t maxread = dirp->allocation;
-	  ssize_t bytes;
-
-	  bytes = __old_getdents64 (dirp->fd, dirp->data, maxread);
+	  ssize_t bytes = __getdents64 (dirp->fd, dirstream_data (dirp),
+					dirstream_alloc_size (dirp));
 	  if (bytes <= 0)
 	    {
 	      /* On some systems getdents fails with ENOENT when the
@@ -149,13 +145,12 @@ __old_readdir64_unlocked (DIR *dirp)
 	  dirp->offset = 0;
 	}
 
-      dp = (struct __old_dirent64 *) &dirp->data[dirp->offset];
-
-      reclen = dp->d_reclen;
-
-      dirp->offset += reclen;
-
-      dirp->filepos = dp->d_off;
+      dp = dirstream_ret_entry64_compat (dirp);
+      if (dp == NULL)
+	{
+	  __set_errno (EOVERFLOW);
+	  break;
+	}
 
       /* Skip deleted files.  */
     } while (dp->d_ino == 0);
-- 
2.17.1