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) 1996-2017, 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 strerror and strerror_r to use the former if it is
58 * available and also return a more useful value (the error string).
59 */
60 char *
pqStrerror(int errnum,char * strerrbuf,size_t buflen)61 pqStrerror(int errnum, char *strerrbuf, size_t buflen)
62 {
63 #if defined(FRONTEND) && defined(ENABLE_THREAD_SAFETY) && defined(HAVE_STRERROR_R)
64 /* reentrant strerror_r is available */
65 #ifdef STRERROR_R_INT
66 /* SUSv3 version */
67 if (strerror_r(errnum, strerrbuf, buflen) == 0)
68 return strerrbuf;
69 else
70 return "Unknown error";
71 #else
72 /* GNU libc */
73 return strerror_r(errnum, strerrbuf, buflen);
74 #endif
75 #else
76 /* no strerror_r() available, just use strerror */
77 strlcpy(strerrbuf, strerror(errnum), buflen);
78
79 return strerrbuf;
80 #endif
81 }
82
83 /*
84 * Wrapper around getpwuid() or getpwuid_r() to mimic POSIX getpwuid_r()
85 * behaviour, if that function is not available or required.
86 *
87 * Per POSIX, the possible cases are:
88 * success: returns zero, *result is non-NULL
89 * uid not found: returns zero, *result is NULL
90 * error during lookup: returns an errno code, *result is NULL
91 * (caller should *not* assume that the errno variable is set)
92 */
93 #ifndef WIN32
94 int
pqGetpwuid(uid_t uid,struct passwd * resultbuf,char * buffer,size_t buflen,struct passwd ** result)95 pqGetpwuid(uid_t uid, struct passwd *resultbuf, char *buffer,
96 size_t buflen, struct passwd **result)
97 {
98 #if defined(FRONTEND) && defined(ENABLE_THREAD_SAFETY) && defined(HAVE_GETPWUID_R)
99 return getpwuid_r(uid, resultbuf, buffer, buflen, result);
100 #else
101 /* no getpwuid_r() available, just use getpwuid() */
102 errno = 0;
103 *result = getpwuid(uid);
104 /* paranoia: ensure we return zero on success */
105 return (*result == NULL) ? errno : 0;
106 #endif
107 }
108 #endif
109
110 /*
111 * Wrapper around gethostbyname() or gethostbyname_r() to mimic
112 * POSIX gethostbyname_r() behaviour, if it is not available or required.
113 * This function is called _only_ by our getaddinfo() portability function.
114 */
115 #ifndef HAVE_GETADDRINFO
116 int
pqGethostbyname(const char * name,struct hostent * resultbuf,char * buffer,size_t buflen,struct hostent ** result,int * herrno)117 pqGethostbyname(const char *name,
118 struct hostent *resultbuf,
119 char *buffer, size_t buflen,
120 struct hostent **result,
121 int *herrno)
122 {
123 #if defined(FRONTEND) && defined(ENABLE_THREAD_SAFETY) && defined(HAVE_GETHOSTBYNAME_R)
124
125 /*
126 * broken (well early POSIX draft) gethostbyname_r() which returns 'struct
127 * hostent *'
128 */
129 *result = gethostbyname_r(name, resultbuf, buffer, buflen, herrno);
130 return (*result == NULL) ? -1 : 0;
131 #else
132
133 /* no gethostbyname_r(), just use gethostbyname() */
134 *result = gethostbyname(name);
135
136 if (*result != NULL)
137 *herrno = h_errno;
138
139 if (*result != NULL)
140 return 0;
141 else
142 return -1;
143 #endif
144 }
145
146 #endif
147