1 /*-------------------------------------------------------------------------
2 *
3 * thread.c
4 *
5 * Prototypes and macros around system calls, used to help make
6 * threaded libraries reentrant and safe to use from threaded applications.
7 *
8 * Portions Copyright (c) 1996-2020, PostgreSQL Global Development Group
9 *
10 * src/port/thread.c
11 *
12 *-------------------------------------------------------------------------
13 */
14
15 #include "c.h"
16
17 #include <pwd.h>
18
19
20 /*
21 * Threading sometimes requires specially-named versions of functions
22 * that return data in static buffers, like strerror_r() instead of
23 * strerror(). Other operating systems use pthread_setspecific()
24 * and pthread_getspecific() internally to allow standard library
25 * functions to return static data to threaded applications. And some
26 * operating systems have neither.
27 *
28 * Additional confusion exists because many operating systems that
29 * use pthread_setspecific/pthread_getspecific() also have *_r versions
30 * of standard library functions for compatibility with operating systems
31 * that require them. However, internally, these *_r functions merely
32 * call the thread-safe standard library functions.
33 *
34 * For example, BSD/OS 4.3 uses Bind 8.2.3 for getpwuid(). Internally,
35 * getpwuid() calls pthread_setspecific/pthread_getspecific() to return
36 * static data to the caller in a thread-safe manner. However, BSD/OS
37 * also has getpwuid_r(), which merely calls getpwuid() and shifts
38 * around the arguments to match the getpwuid_r() function declaration.
39 * Therefore, while BSD/OS has getpwuid_r(), it isn't required. It also
40 * doesn't have strerror_r(), so we can't fall back to only using *_r
41 * functions for threaded programs.
42 *
43 * The current setup is to try threading in this order:
44 *
45 * use *_r function names if they exit
46 * (*_THREADSAFE=yes)
47 * use non-*_r functions if they are thread-safe
48 *
49 * One thread-safe solution for gethostbyname() might be to use getaddrinfo().
50 *
51 * Run src/test/thread to test if your operating system has thread-safe
52 * non-*_r functions.
53 */
54
55
56 /*
57 * Wrapper around getpwuid() or getpwuid_r() to mimic POSIX getpwuid_r()
58 * behaviour, if that function is not available or required.
59 *
60 * Per POSIX, the possible cases are:
61 * success: returns zero, *result is non-NULL
62 * uid not found: returns zero, *result is NULL
63 * error during lookup: returns an errno code, *result is NULL
64 * (caller should *not* assume that the errno variable is set)
65 */
66 #ifndef WIN32
67 int
pqGetpwuid(uid_t uid,struct passwd * resultbuf,char * buffer,size_t buflen,struct passwd ** result)68 pqGetpwuid(uid_t uid, struct passwd *resultbuf, char *buffer,
69 size_t buflen, struct passwd **result)
70 {
71 #if defined(FRONTEND) && defined(ENABLE_THREAD_SAFETY) && defined(HAVE_GETPWUID_R)
72 return getpwuid_r(uid, resultbuf, buffer, buflen, result);
73 #else
74 /* no getpwuid_r() available, just use getpwuid() */
75 errno = 0;
76 *result = getpwuid(uid);
77 /* paranoia: ensure we return zero on success */
78 return (*result == NULL) ? errno : 0;
79 #endif
80 }
81 #endif
82
83 /*
84 * Wrapper around gethostbyname() or gethostbyname_r() to mimic
85 * POSIX gethostbyname_r() behaviour, if it is not available or required.
86 * This function is called _only_ by our getaddrinfo() portability function.
87 */
88 #ifndef HAVE_GETADDRINFO
89 int
pqGethostbyname(const char * name,struct hostent * resultbuf,char * buffer,size_t buflen,struct hostent ** result,int * herrno)90 pqGethostbyname(const char *name,
91 struct hostent *resultbuf,
92 char *buffer, size_t buflen,
93 struct hostent **result,
94 int *herrno)
95 {
96 #if defined(FRONTEND) && defined(ENABLE_THREAD_SAFETY) && defined(HAVE_GETHOSTBYNAME_R)
97
98 /*
99 * broken (well early POSIX draft) gethostbyname_r() which returns 'struct
100 * hostent *'
101 */
102 *result = gethostbyname_r(name, resultbuf, buffer, buflen, herrno);
103 return (*result == NULL) ? -1 : 0;
104 #else
105
106 /* no gethostbyname_r(), just use gethostbyname() */
107 *result = gethostbyname(name);
108
109 if (*result != NULL)
110 *herrno = h_errno;
111
112 if (*result != NULL)
113 return 0;
114 else
115 return -1;
116 #endif
117 }
118
119 #endif
120