glibc/sysdeps/unix/sysv/linux/getdents.c

/* Copyright (C) 1993, 95, 96, 97, 98, 99, 2000 Free Software Foundation, Inc.
   This file is part of the GNU C Library.

   The GNU C Library is free software; you can redistribute it and/or
   modify it under the terms of the GNU Library General Public License as
   published by the Free Software Foundation; either version 2 of the
   License, or (at your option) any later version.

   The GNU C Library is distributed in the hope that it will be useful,
   but WITHOUT ANY WARRANTY; without even the implied warranty of
   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
   Library General Public License for more details.

   You should have received a copy of the GNU Library General Public
   License along with the GNU C Library; see the file COPYING.LIB.  If not,
   write to the Free Software Foundation, Inc., 59 Temple Place - Suite 330,
   Boston, MA 02111-1307, USA.  */

#include <alloca.h>
#include <assert.h>
#include <errno.h>
#include <dirent.h>
#include <stddef.h>
#include <string.h>
#include <unistd.h>
#include <sys/param.h>
#include <sys/types.h>

#include <sysdep.h>
#include <sys/syscall.h>
#include <bp-checks.h>

#include <linux/posix_types.h>

#include "kernel-features.h"

#ifdef __NR_getdents64
#ifndef __ASSUME_GETDENTS64_SYSCALL
#ifndef __GETDENTS
/* The variable is shared between all *getdents* calls.  */
int __have_no_getdents64;
#else
extern int __have_no_getdents64;
#endif
#endif
#endif

#define offsetof(TYPE, MEMBER) ((size_t) &((TYPE *)0)->MEMBER)

extern int __syscall_getdents (int fd, char *__unbounded buf, size_t nbytes);

/* For Linux we need a special version of this file since the
   definition of `struct dirent' is not the same for the kernel and
   the libc.  There is one additional field which might be introduced
   in the kernel structure in the future.

   Here is the kernel definition of `struct dirent' as of 2.1.20:  */

struct kernel_dirent
  {
    long int d_ino;
    __kernel_off_t d_off;
    unsigned short int d_reclen;
    char d_name[256];
  };

struct kernel_dirent64
  {
    u_int64_t		d_ino;
    int64_t		d_off;
    unsigned short int	d_reclen;
    unsigned char	d_type;
    char		d_name[256];
  };

#ifndef __GETDENTS
# define __GETDENTS __getdents
#endif
#ifndef DIRENT_TYPE
# define DIRENT_TYPE struct dirent
#endif
#ifndef DIRENT_SET_DP_INO
# define DIRENT_SET_DP_INO(dp, value) (dp)->d_ino = (value)
#endif

/* The problem here is that we cannot simply read the next NBYTES
   bytes.  We need to take the additional field into account.  We use
   some heuristic.  Assuming the directory contains names with 14
   characters on average we can compute an estimated number of entries
   which fit in the buffer.  Taking this number allows us to specify a
   reasonable number of bytes to read.  If we should be wrong, we can
   reset the file descriptor.  In practice the kernel is limiting the
   amount of data returned much more then the reduced buffer size.  */
ssize_t
internal_function
__GETDENTS (int fd, char *buf, size_t nbytes)
{
  DIRENT_TYPE *dp;
  off_t last_offset = -1;
  ssize_t retval;

#ifdef __NR_getdents64
#ifndef __ASSUME_GETDENTS64_SYSCALL
  if (!__have_no_getdents64)
#endif
    {
#ifndef __ASSUME_GETDENTS64_SYSCALL
      int saved_errno = errno;
#endif
      char *kbuf = buf;
      size_t kbytes = nbytes;
      if (offsetof (DIRENT_TYPE, d_name)
	  < offsetof (struct kernel_dirent64, d_name)
	  && nbytes <= sizeof (DIRENT_TYPE))
	{
	  kbytes = nbytes + offsetof (struct kernel_dirent64, d_name)
		   - offsetof (DIRENT_TYPE, d_name);
	  kbuf = __alloca(kbytes);
	}
      retval = INLINE_SYSCALL (getdents64, 3, fd, CHECK_N(kbuf, kbytes),
			       kbytes);
#ifndef __ASSUME_GETDENTS64_SYSCALL
      if (retval != -1 && errno != -EINVAL)
#endif
	{
	  struct kernel_dirent64 *kdp;
	  const size_t size_diff = (offsetof (struct kernel_dirent64, d_name)
				   - offsetof (DIRENT_TYPE, d_name));

	  /* If the structure returned by the kernel is identical to what we
	     need, don't do any conversions.  */
	  if (offsetof (DIRENT_TYPE, d_name)
	      == offsetof (struct kernel_dirent64, d_name)
	      && sizeof (dp->d_ino) == sizeof (kdp->d_ino)
	      && sizeof (dp->d_off) == sizeof (kdp->d_off))
	    return retval;

	  dp = (DIRENT_TYPE *)buf;
	  kdp = (struct kernel_dirent64 *)kbuf;
	  while ((char *) kdp < kbuf + retval)
	    {
	      const size_t alignment = __alignof__ (DIRENT_TYPE);
	      /* Since kdp->d_reclen is already aligned for the kernel
		 structure this may compute a value that is bigger
		 than necessary.  */
	      size_t old_reclen = kdp->d_reclen;
	      size_t new_reclen = ((old_reclen - size_diff + alignment - 1)
				  & ~(alignment - 1));
	      u_int64_t d_ino = kdp->d_ino;
	      int64_t d_off = kdp->d_off;
	      unsigned char d_type = kdp->d_type;

	      DIRENT_SET_DP_INO(dp, d_ino);
	      dp->d_off = d_off;
	      if ((sizeof (dp->d_ino) != sizeof (kdp->d_ino)
		   && dp->d_ino != d_ino)
		  || (sizeof (dp->d_off) != sizeof (kdp->d_off)
		      && dp->d_off != d_off))
		{
		  /* Overflow.  If there was at least one entry
		     before this one, return them without error,
		     otherwise signal overflow.  */
		  if (last_offset != -1)
		    {
		      __lseek (fd, last_offset, SEEK_SET);
		      return (char *) dp - buf;
		    }
		  __set_errno (EOVERFLOW);
		  return -1;
		}

	      last_offset = d_off;
	      dp->d_reclen = new_reclen;
	      dp->d_type = d_type;
	      memmove (dp->d_name, kdp->d_name,
		       old_reclen - offsetof (struct kernel_dirent64, d_name));

	      dp = (DIRENT_TYPE *) ((char *) dp + new_reclen);
	      kdp = (struct kernel_dirent64 *) ((char *) kdp + old_reclen);
	    }

	  return (char *) dp - buf;
	}

#ifndef __ASSUME_GETDENTS64_SYSCALL
      __set_errno (saved_errno);
      __have_no_getdents64 = 1;
#endif
    }
#endif
  {
    size_t red_nbytes;
    struct kernel_dirent *skdp, *kdp;
    const size_t size_diff = (offsetof (DIRENT_TYPE, d_name)
			      - offsetof (struct kernel_dirent, d_name));

    red_nbytes = MIN (nbytes
		      - ((nbytes / (offsetof (DIRENT_TYPE, d_name) + 14))
			 * size_diff),
		      nbytes - size_diff);

    dp = (DIRENT_TYPE *) buf;
    skdp = kdp = __alloca (red_nbytes);

    retval = INLINE_SYSCALL (getdents, 3, fd,
			     CHECK_N ((char *) kdp, red_nbytes), red_nbytes);

    if (retval == -1)
      return -1;

    while ((char *) kdp < (char *) skdp + retval)
      {
	const size_t alignment = __alignof__ (DIRENT_TYPE);
	/* Since kdp->d_reclen is already aligned for the kernel structure
	   this may compute a value that is bigger than necessary.  */
	size_t new_reclen = ((kdp->d_reclen + size_diff + alignment - 1)
			     & ~(alignment - 1));
	if ((char *) dp + new_reclen > buf + nbytes)
	  {
	    /* Our heuristic failed.  We read too many entries.  Reset
	       the stream.  */
	    assert (last_offset != -1);
	    __lseek (fd, last_offset, SEEK_SET);

	    if ((char *) dp == buf)
	      {
		/* The buffer the user passed in is too small to hold even
		   one entry.  */
		__set_errno (EINVAL);
		return -1;
	      }

	    break;
	  }

	last_offset = kdp->d_off;
	DIRENT_SET_DP_INO(dp, kdp->d_ino);
	dp->d_off = kdp->d_off;
	dp->d_reclen = new_reclen;
	dp->d_type = DT_UNKNOWN;
	memcpy (dp->d_name, kdp->d_name,
		kdp->d_reclen - offsetof (struct kernel_dirent, d_name));

	dp = (DIRENT_TYPE *) ((char *) dp + new_reclen);
	kdp = (struct kernel_dirent *) (((char *) kdp) + kdp->d_reclen);
      }
    }

  return (char *) dp - buf;
}