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libvirt/tests/virmockstathelpers.c
Daniel P. Berrangé ff376c6283 tests: fix mocking of stat() / lstat() functions 
Quite a few of the tests have a need to mock the stat() / lstat()
functions and they are taking somewhat different & inconsistent
approaches none of which are actually fully correct. This is shown
by fact that 'make check' fails on 32-bit hosts. Investigation
revealed that the code was calling into the native C library impl,
not getting intercepted by our mocks.

The POSIX stat() function might resolve to any number of different
symbols in the C library.

The may be an additional stat64() function exposed by the headers
too.

On 64-bit hosts the stat & stat64 functions are identical, always
refering to the 64-bit ABI.

On 32-bit hosts they refer to the 32-bit & 64-bit ABIs respectively.

Libvirt uses _FILE_OFFSET_BITS=64 on 32-bit hosts, which causes the
C library to transparently rewrite stat() calls to be stat64() calls.
Libvirt will never see the 32-bit ABI from the traditional stat()
call. We cannot assume this rewriting is done using a macro. It might
be, but on GLibC it is done with a magic __asm__ statement to apply
the rewrite at link time instead of at preprocessing.

In GLibC there may be two additional functions exposed by the headers,
__xstat() and __xstat64(). When these exist, stat() and stat64() are
transparently rewritten to call __xstat() and __xstat64() respectively.
The former symbols will not actally exist in the library at all, only
the header. The leading "__" indicates the symbols are a private impl
detail of the C library that applications should not care about.
Unfortunately, because we are trying to mock replace the C library,
we need to know about this internal impl detail.

With all this in mind the list of functions we have to mock will depend
on several factors

 - If _FILE_OFFSET_BITS is set, then we are on a 32-bit host, and we
   only need to mock stat64 and __xstat64. The other stat / __xstat
   functions exist, but we'll never call them so they can be ignored
   for mocking.

 - If _FILE_OFFSET_BITS is not set, then we are on a 64-bit host and
   we should mock stat, stat64, __xstat & __xstat64. Either may be
   called by app code.

 - If __xstat & __xstat64 exist, then stat & stat64 will not exist
   as symbols in the library, so the latter should not be mocked.

The same all applies to lstat()

These rules are complex enough that we don't want to duplicate them
across every mock file, so this centralizes all the logic in a helper
file virmockstathelper.c that should be #included when needed. The
code merely need to provide a filename rewriting callback called
virMockStatRedirect(). Optionally VIR_MOCK_STAT_HOOK can be defined
as a macro if further processing is needed inline.

Signed-off-by: Daniel P. Berrangé <berrange@redhat.com>
2019-04-03 11:31:38 +01:00

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/*
* Copyright (C) 2019 Red Hat, Inc.
*
* This library is free software; you can redistribute it and/or
* modify it under the terms of the GNU Lesser General Public
* License as published by the Free Software Foundation; either
* version 2.1 of the License, or (at your option) any later version.
*
* This 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
* Lesser General Public License for more details.
*
* You should have received a copy of the GNU Lesser General Public
* License along with this library. If not, see
* <http://www.gnu.org/licenses/>.
*
* Helpers for dealing with the many variants of stat(). This
* C file should be included from any file that wants to mock
* stat() correctly.
*/
#include "virmock.h"
#include "viralloc.h"
#include <sys/stat.h>
#include <unistd.h>
/*
* The POSIX stat() function might resolve to any number of different
* symbols in the C library.
*
* The may be an additional stat64() function exposed by the headers
* too.
*
* On 64-bit hosts the stat & stat64 functions are identical, always
* refering to the 64-bit ABI.
*
* On 32-bit hosts they refer to the 32-bit & 64-bit ABIs respectively.
*
* Libvirt uses _FILE_OFFSET_BITS=64 on 32-bit hosts, which causes the
* C library to transparently rewrite stat() calls to be stat64() calls.
* Libvirt will never see the 32-bit ABI from the traditional stat()
* call. We cannot assume this rewriting is done using a macro. It might
* be, but on GLibC it is done with a magic __asm__ statement to apply
* the rewrite at link time instead of at preprocessing.
*
* In GLibC there may be two additional functions exposed by the headers,
* __xstat() and __xstat64(). When these exist, stat() and stat64() are
* transparently rewritten to call __xstat() and __xstat64() respectively.
* The former symbols will not actally exist in the library at all, only
* the header. The leading "__" indicates the symbols are a private impl
* detail of the C library that applications should not care about.
* Unfortunately, because we are trying to mock replace the C library,
* we need to know about this internal impl detail.
*
* With all this in mind the list of functions we have to mock will depend
* on several factors
*
* - If _FILE_OFFSET_BITS is set, then we are on a 32-bit host, and we
* only need to mock stat64 and __xstat64. The other stat / __xstat
* functions exist, but we'll never call them so they can be ignored
* for mocking.
*
* - If _FILE_OFFSET_BITS is not set, then we are on a 64-bit host and
* we should mock stat, stat64, __xstat & __xstat64. Either may be
* called by app code.
*
* - If __xstat & __xstat64 exist, then stat & stat64 will not exist
* as symbols in the library, so the latter should not be mocked.
*
* The same all applies to lstat()
*/
#if defined(HAVE_STAT) && !defined(HAVE___XSTAT) && !defined(_FILE_OFFSET_BITS)
# define MOCK_STAT
#endif
#if defined(HAVE_STAT64) && !defined(HAVE___XSTAT64)
# define MOCK_STAT64
#endif
#if defined(HAVE___XSTAT) && !defined(_FILE_OFFSET_BITS)
# define MOCK___XSTAT
#endif
#if defined(HAVE___XSTAT64)
# define MOCK___XSTAT64
#endif
#if defined(HAVE_LSTAT) && !defined(HAVE___LXSTAT) && !defined(_FILE_OFFSET_BITS)
# define MOCK_LSTAT
#endif
#if defined(HAVE_LSTAT64) && !defined(HAVE___LXSTAT64)
# define MOCK_LSTAT64
#endif
#if defined(HAVE___LXSTAT) && !defined(_FILE_OFFSET_BITS)
# define MOCK___LXSTAT
#endif
#if defined(HAVE___LXSTAT64)
# define MOCK___LXSTAT64
#endif
#ifdef MOCK_STAT
static int (*real_stat)(const char *path, struct stat *sb);
#endif
#ifdef MOCK_STAT64
static int (*real_stat64)(const char *path, struct stat64 *sb);
#endif
#ifdef MOCK___XSTAT
static int (*real___xstat)(int ver, const char *path, struct stat *sb);
#endif
#ifdef MOCK___XSTAT64
static int (*real___xstat64)(int ver, const char *path, struct stat64 *sb);
#endif
#ifdef MOCK_LSTAT
static int (*real_lstat)(const char *path, struct stat *sb);
#endif
#ifdef MOCK_LSTAT64
static int (*real_lstat64)(const char *path, struct stat64 *sb);
#endif
#ifdef MOCK___LXSTAT
static int (*real___lxstat)(int ver, const char *path, struct stat *sb);
#endif
#ifdef MOCK___LXSTAT64
static int (*real___lxstat64)(int ver, const char *path, struct stat64 *sb);
#endif
static bool init;
static bool debug;
#define fdebug(msg, ...) do { if (debug) fprintf(stderr, msg, __VA_ARGS__); } while (0)
static void virMockStatInit(void)
{
if (init)
return;
init = true;
debug = getenv("VIR_MOCK_STAT_DEBUG");
#ifdef MOCK_STAT
VIR_MOCK_REAL_INIT(stat);
fdebug("real stat %p\n", real_stat);
#endif
#ifdef MOCK_STAT64
VIR_MOCK_REAL_INIT(stat64);
fdebug("real stat64 %p\n", real_stat64);
#endif
#ifdef MOCK___XSTAT
VIR_MOCK_REAL_INIT(__xstat);
fdebug("real __xstat %p\n", real___xstat);
#endif
#ifdef MOCK___XSTAT64
VIR_MOCK_REAL_INIT(__xstat64);
fdebug("real __xstat64 %p\n", real___xstat64);
#endif
#ifdef MOCK_LSTAT
VIR_MOCK_REAL_INIT(lstat);
fdebug("real lstat %p\n", real_lstat);
#endif
#ifdef MOCK_LSTAT64
VIR_MOCK_REAL_INIT(lstat64);
fdebug("real lstat64 %p\n", real_lstat64);
#endif
#ifdef MOCK___LXSTAT
VIR_MOCK_REAL_INIT(__lxstat);
fdebug("real __lxstat %p\n", real___lxstat);
#endif
#ifdef MOCK___LXSTAT64
VIR_MOCK_REAL_INIT(__lxstat64);
fdebug("real __lxstat64 %p\n", real___lxstat64);
#endif
}
/*
* @stat: the path being queried
* @newpath: fill with redirected path, or leave NULL to use orig path
*
* Return 0 on success, -1 on allocation error
*/
static int virMockStatRedirect(const char *path, char **newpath);
#ifndef VIR_MOCK_STAT_HOOK
# define VIR_MOCK_STAT_HOOK do { } while (0)
#endif
#ifdef MOCK_STAT
int stat(const char *path, struct stat *sb)
{
VIR_AUTOFREE(char *) newpath = NULL;
virMockStatInit();
if (virMockStatRedirect(path, &newpath) < 0)
abort();
fdebug("stat redirect %s to %s sb=%p\n", path, newpath ? newpath : path, sb);
VIR_MOCK_STAT_HOOK;
return real_stat(newpath ? newpath : path, sb);
}
#endif
#ifdef MOCK_STAT64
int stat64(const char *path, struct stat64 *sb)
{
VIR_AUTOFREE(char *) newpath = NULL;
virMockStatInit();
if (virMockStatRedirect(path, &newpath) < 0)
abort();
fdebug("stat64 redirect %s to %s sb=%p\n", path, newpath ? newpath : path, sb);
VIR_MOCK_STAT_HOOK;
return real_stat64(newpath ? newpath : path, sb);
}
#endif
#ifdef MOCK___XSTAT
int
__xstat(int ver, const char *path, struct stat *sb)
{
VIR_AUTOFREE(char *) newpath = NULL;
virMockStatInit();
if (virMockStatRedirect(path, &newpath) < 0)
abort();
fdebug("__xstat redirect %s to %s sb=%p\n", path, newpath ? newpath : path, sb);
VIR_MOCK_STAT_HOOK;
return real___xstat(ver, newpath ? newpath : path, sb);
}
#endif
#ifdef MOCK___XSTAT64
int
__xstat64(int ver, const char *path, struct stat64 *sb)
{
VIR_AUTOFREE(char *) newpath = NULL;
virMockStatInit();
if (virMockStatRedirect(path, &newpath) < 0)
abort();
fdebug("__xstat64 redirect %s to %s sb=%p\n", path, newpath ? newpath : path, sb);
VIR_MOCK_STAT_HOOK;
return real___xstat64(ver, newpath ? newpath : path, sb);
}
#endif
#ifdef MOCK_LSTAT
int
lstat(const char *path, struct stat *sb)
{
VIR_AUTOFREE(char *) newpath = NULL;
virMockStatInit();
if (virMockStatRedirect(path, &newpath) < 0)
abort();
fdebug("lstat redirect %s to %s sb=%p\n", path, newpath ? newpath : path, sb);
VIR_MOCK_STAT_HOOK;
return real_lstat(newpath ? newpath : path, sb);
}
#endif
#ifdef MOCK_LSTAT64
int
lstat64(const char *path, struct stat64 *sb)
{
VIR_AUTOFREE(char *) newpath = NULL;
virMockStatInit();
if (virMockStatRedirect(path, &newpath) < 0)
abort();
fdebug("lstat64 redirect %s to %s sb=%p\n", path, newpath ? newpath : path, sb);
VIR_MOCK_STAT_HOOK;
return real_lstat64(newpath ? newpath : path, sb);
}
#endif
#ifdef MOCK___LXSTAT
int
__lxstat(int ver, const char *path, struct stat *sb)
{
VIR_AUTOFREE(char *) newpath = NULL;
virMockStatInit();
if (virMockStatRedirect(path, &newpath) < 0)
abort();
fdebug("__lxstat redirect %s to %s sb=%p\n", path, newpath ? newpath : path, sb);
VIR_MOCK_STAT_HOOK;
return real___lxstat(ver, newpath ? newpath : path, sb);
}
#endif
#ifdef MOCK___LXSTAT64
int
__lxstat64(int ver, const char *path, struct stat64 *sb)
{
VIR_AUTOFREE(char *) newpath = NULL;
virMockStatInit();
if (virMockStatRedirect(path, &newpath) < 0)
abort();
fdebug("__lxstat64 redirect %s to %s sb=%p\n", path, newpath ? newpath : path, sb);
VIR_MOCK_STAT_HOOK;
return real___lxstat64(ver, newpath ? newpath : path, sb);
}
#endif
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