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4186c9f42b
* sysdeps/unix/sysv/linux/getdents.c (__getdents): Avoid initial lseek call be passing in a buffer which never allow a successful first getdents syscall if not at leas the initial entry can be stored in the user buffer.
131 lines
4.1 KiB
C
131 lines
4.1 KiB
C
/* Copyright (C) 1993, 95, 96, 97, 98, 99, 2000 Free Software Foundation, Inc.
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This file is part of the GNU C Library.
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The GNU C Library is free software; you can redistribute it and/or
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modify it under the terms of the GNU Library General Public License as
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published by the Free Software Foundation; either version 2 of the
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License, or (at your option) any later version.
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The GNU C Library is distributed in the hope that it will be useful,
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but WITHOUT ANY WARRANTY; without even the implied warranty of
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MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
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Library General Public License for more details.
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You should have received a copy of the GNU Library General Public
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License along with the GNU C Library; see the file COPYING.LIB. If not,
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write to the Free Software Foundation, Inc., 59 Temple Place - Suite 330,
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Boston, MA 02111-1307, USA. */
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#include <alloca.h>
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#include <assert.h>
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#include <errno.h>
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#include <dirent.h>
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#include <stddef.h>
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#include <string.h>
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#include <unistd.h>
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#include <sys/param.h>
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#include <sys/types.h>
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#include <sysdep.h>
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#include <sys/syscall.h>
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#include <linux/posix_types.h>
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#define offsetof(TYPE, MEMBER) ((size_t) &((TYPE *)0)->MEMBER)
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extern int __syscall_getdents (int fd, char *buf, size_t nbytes);
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/* For Linux we need a special version of this file since the
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definition of `struct dirent' is not the same for the kernel and
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the libc. There is one additional field which might be introduced
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in the kernel structure in the future.
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Here is the kernel definition of `struct dirent' as of 2.1.20: */
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struct kernel_dirent
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{
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long int d_ino;
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__kernel_off_t d_off;
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unsigned short int d_reclen;
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char d_name[256];
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};
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#ifdef GETDENTS64
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# define __getdents __getdents64
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# define dirent dirent64
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#endif
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/* The problem here is that we cannot simply read the next NBYTES
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bytes. We need to take the additional field into account. We use
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some heuristic. Assuming the directory contains names with 14
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characters on average we can compute an estimated number of entries
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which fit in the buffer. Taking this number allows us to specify a
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reasonable number of bytes to read. If we should be wrong, we can
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reset the file descriptor. In practice the kernel is limiting the
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amount of data returned much more then the reduced buffer size. */
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ssize_t
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internal_function
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__getdents (int fd, char *buf, size_t nbytes)
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{
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off_t last_offset = -1;
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size_t red_nbytes;
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struct kernel_dirent *skdp, *kdp;
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struct dirent *dp;
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int retval;
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const size_t size_diff = (offsetof (struct dirent, d_name)
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- offsetof (struct kernel_dirent, d_name));
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red_nbytes = MIN (nbytes
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- ((nbytes / (offsetof (struct dirent, d_name) + 14))
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* size_diff),
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nbytes - size_diff);
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dp = (struct dirent *) buf;
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skdp = kdp = __alloca (red_nbytes);
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retval = INLINE_SYSCALL (getdents, 3, fd, (char *) kdp, red_nbytes);
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if (retval == -1)
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return -1;
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while ((char *) kdp < (char *) skdp + retval)
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{
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const size_t alignment = __alignof__ (struct dirent);
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/* Since kdp->d_reclen is already aligned for the kernel structure
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this may compute a value that is bigger than necessary. */
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size_t new_reclen = ((kdp->d_reclen + size_diff + alignment - 1)
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& ~(alignment - 1));
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if ((char *) dp + new_reclen > buf + nbytes)
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{
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/* Our heuristic failed. We read too many entries. Reset
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the stream. */
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assert (last_offset != -1);
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__lseek (fd, last_offset, SEEK_SET);
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if ((char *) dp == buf)
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{
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/* The buffer the user passed in is too small to hold even
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one entry. */
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__set_errno (EINVAL);
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return -1;
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}
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break;
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}
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last_offset = kdp->d_off;
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dp->d_ino = kdp->d_ino;
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dp->d_off = kdp->d_off;
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dp->d_reclen = new_reclen;
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dp->d_type = DT_UNKNOWN;
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memcpy (dp->d_name, kdp->d_name,
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kdp->d_reclen - offsetof (struct kernel_dirent, d_name));
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dp = (struct dirent *) ((char *) dp + new_reclen);
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kdp = (struct kernel_dirent *) (((char *) kdp) + kdp->d_reclen);
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}
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return (char *) dp - buf;
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}
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