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Fix Linux getcwd for long paths

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The getcwd syscall (so far?) can only handle path up to one page
in size.  There is no limit about directory hierarchy depth, though,
and the POSIX getcwd is supposed to handle this.  In that case fall
back to the generic getcwd.

Additionally, optimize the generic getcwd to use openat when possible
to change the asymptotic performance from O(N^2) to O(n).
This commit is contained in:
Ulrich Drepper
2011-05-08 08:37:19 -04:00
parent 28377d1bf5
commit 7fb90fb89b
11 changed files with 320 additions and 159 deletions
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61
sysdeps/unix/sysv/linux/getcwd.c
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@@ -1,5 +1,5 @@
/* Determine current working directory. Linux version.
Copyright (C) 1997,1998,1999,2000,2002,2003,2006
Copyright (C) 1997,1998,1999,2000,2002,2003,2006,2011
Free Software Foundation, Inc.
This file is part of the GNU C Library.
Contributed by Ulrich Drepper <drepper@cygnus.com>, 1997.
@@ -45,20 +45,13 @@
compiling under 2.1.92+ the libc still runs under older kernels. */
# define no_syscall_getcwd 0
# define have_new_dcache 1
/* This is a trick since we don't define generic_getcwd. */
# define generic_getcwd getcwd
#else
/* The "proc" filesystem provides an easy method to retrieve the value.
For each process, the corresponding directory contains a symbolic link
named `cwd'. Reading the content of this link immediate gives us the
information. But we have to take care for systems which do not have
the proc filesystem mounted. Use the POSIX implementation in this case. */
static char *generic_getcwd (char *buf, size_t size) internal_function;
# if __NR_getcwd
/* Kernel 2.1.92 introduced a third way to get the current working
directory: a syscall. We've got to be careful that even when
compiling under 2.1.92+ the libc still runs under older kernels. */
compiling under 2.1.92+ the libc still runs under older kernels.
An additional problem is that the system call does not return
the path of directories longer than one page. */
static int no_syscall_getcwd;
static int have_new_dcache;
# else
@@ -67,6 +60,13 @@ static int have_new_dcache = 1;
# endif
#endif
/* The "proc" filesystem provides an easy method to retrieve the value.
For each process, the corresponding directory contains a symbolic link
named `cwd'. Reading the content of this link immediate gives us the
information. But we have to take care for systems which do not have
the proc filesystem mounted. Use the POSIX implementation in this case. */
static char *generic_getcwd (char *buf, size_t size) internal_function;
char *
__getcwd (char *buf, size_t size)
{
@@ -124,6 +124,33 @@ __getcwd (char *buf, size_t size)
return buf;
}
// XXX This should not be necessary but the full getcwd implementation
// drags in too much for the current build proces of ld.so to handle
#ifndef NOT_IN_libc
/* The system call cannot handle paths longer than a page.
Neither can the magic symlink in /proc/self. Just use the
generic implementation right away. */
if (errno == ENAMETOOLONG)
{
# ifndef NO_ALLOCATION
if (buf == NULL && size == 0)
{
free (path);
path = NULL;
}
# endif
result = generic_getcwd (path, size);
# ifndef NO_ALLOCATION
if (result == NULL && buf == NULL && size != 0)
free (path);
# endif
return result;
}
#endif
# if __ASSUME_GETCWD_SYSCALL
/* It should never happen that the `getcwd' syscall failed because
the buffer is too small if we allocated the buffer ourselves
@@ -196,7 +223,7 @@ __getcwd (char *buf, size_t size)
#ifndef NO_ALLOCATION
/* Don't put restrictions on the length of the path unless the user does. */
if (size == 0)
if (buf == NULL && size == 0)
{
free (path);
path = NULL;
@@ -214,9 +241,11 @@ __getcwd (char *buf, size_t size)
}
weak_alias (__getcwd, getcwd)
#if __ASSUME_GETCWD_SYSCALL == 0
// XXX This should not be necessary but the full getcwd implementation
// drags in too much for the current build proces of ld.so to handle
#ifndef NOT_IN_libc
/* Get the code for the generic version. */
# define GETCWD_RETURN_TYPE static char * internal_function
# define __getcwd generic_getcwd
# include <sysdeps/posix/getcwd.c>
#define GETCWD_RETURN_TYPE static char * internal_function
#define __getcwd generic_getcwd
#include <sysdeps/posix/getcwd.c>
#endif