1FPATHCONF(P) POSIX Programmer's Manual FPATHCONF(P)
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6 fpathconf, pathconf - get configurable pathname variables
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9 #include <unistd.h>
10 long fpathconf(int fildes, int name);
12 long pathconf(const char *path, int name);
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16 The fpathconf() and pathconf() functions shall determine the current
17 value of a configurable limit or option (variable) that is associated
18 with a file or directory.
19 For pathconf(), the path argument points to the pathname of a file or
21 directory.
22 For fpathconf(), the fildes argument is an open file descriptor.
24 The name argument represents the variable to be queried relative to
26 that file or directory. Implementations shall support all of the vari‐
27 ables listed in the following table and may support others. The vari‐
28 ables in the following table come from <limits.h> or <unistd.h> and the
29 symbolic constants, defined in <unistd.h>, are the corresponding values
30 used for name.
31 Variable Value of name Requirements
33 {FILESIZEBITS} _PC_FILESIZEBITS 3,4
34 {LINK_MAX} _PC_LINK_MAX 1
35 {MAX_CANON} _PC_MAX_CANON 2
36 {MAX_INPUT} _PC_MAX_INPUT 2
37 {NAME_MAX} _PC_NAME_MAX 3,4
38 {PATH_MAX} _PC_PATH_MAX 4,5
39 {PIPE_BUF} _PC_PIPE_BUF 6
40 {POSIX_ALLOC_SIZE_MIN} _PC_ALLOC_SIZE_MIN
41 {POSIX_REC_INCR_XFER_SIZE} _PC_REC_INCR_XFER_SIZE
42 {POSIX_REC_MAX_XFER_SIZE} _PC_REC_MAX_XFER_SIZE
43 {POSIX_REC_MIN_XFER_SIZE} _PC_REC_MIN_XFER_SIZE
44 {POSIX_REC_XFER_ALIGN} _PC_REC_XFER_ALIGN
45 {SYMLINK_MAX} _PC_SYMLINK_MAX 4,9
46 _POSIX_CHOWN_RESTRICTED _PC_CHOWN_RESTRICTED 7
47 _POSIX_NO_TRUNC _PC_NO_TRUNC 3,4
48 _POSIX_VDISABLE _PC_VDISABLE 2
49 _POSIX_ASYNC_IO _PC_ASYNC_IO 8
50 _POSIX_PRIO_IO _PC_PRIO_IO 8
51 _POSIX_SYNC_IO _PC_SYNC_IO 8
52 Requirements
54 1. If path or fildes refers to a directory, the value returned shall
55 apply to the directory itself.
56 2. If path or fildes does not refer to a terminal file, it is unspeci‐
58 fied whether an implementation supports an association of the vari‐
59 able name with the specified file.
60 3. If path or fildes refers to a directory, the value returned shall
62 apply to filenames within the directory.
63 4. If path or fildes does not refer to a directory, it is unspecified
65 whether an implementation supports an association of the variable
66 name with the specified file.
67 5. If path or fildes refers to a directory, the value returned shall
69 be the maximum length of a relative pathname when the specified
70 directory is the working directory.
71 6. If path refers to a FIFO, or fildes refers to a pipe or FIFO, the
73 value returned shall apply to the referenced object. If path or
74 fildes refers to a directory, the value returned shall apply to any
75 FIFO that exists or can be created within the directory. If path or
76 fildes refers to any other type of file, it is unspecified whether
77 an implementation supports an association of the variable name with
78 the specified file.
79 7. If path or fildes refers to a directory, the value returned shall
81 apply to any files, other than directories, that exist or can be
82 created within the directory.
83 8. If path or fildes refers to a directory, it is unspecified whether
85 an implementation supports an association of the variable name with
86 the specified file.
87 9. If path or fildes refers to a directory, the value returned shall
89 be the maximum length of the string that a symbolic link in that
90 directory can contain.
91
93 If name is an invalid value, both pathconf() and fpathconf() shall
94 return -1 and set errno to indicate the error.
95 If the variable corresponding to name has no limit for the path or file
97 descriptor, both pathconf() and fpathconf() shall return -1 without
98 changing errno. If the implementation needs to use path to determine
99 the value of name and the implementation does not support the associa‐
100 tion of name with the file specified by path, or if the process did not
101 have appropriate privileges to query the file specified by path, or
102 path does not exist, pathconf() shall return -1 and set errno to indi‐
103 cate the error.
104 If the implementation needs to use fildes to determine the value of
106 name and the implementation does not support the association of name
107 with the file specified by fildes, or if fildes is an invalid file
108 descriptor, fpathconf() shall return -1 and set errno to indicate the
109 error.
110 Otherwise, pathconf() or fpathconf() shall return the current variable
112 value for the file or directory without changing errno. The value
113 returned shall not be more restrictive than the corresponding value
114 available to the application when it was compiled with the implementa‐
115 tion's <limits.h> or <unistd.h>.
116
118 The pathconf() function shall fail if:
119 EINVAL The value of name is not valid.
121 ELOOP A loop exists in symbolic links encountered during resolution of
123 the path argument.
124 The pathconf() function may fail if:
127 EACCES Search permission is denied for a component of the path prefix.
129 EINVAL The implementation does not support an association of the vari‐
131 able name with the specified file.
132 ELOOP More than {SYMLOOP_MAX} symbolic links were encountered during
134 resolution of the path argument.
135 ENAMETOOLONG
137 The length of the path argument exceeds {PATH_MAX} or a pathname
138 component is longer than {NAME_MAX}.
139 ENAMETOOLONG
141 As a result of encountering a symbolic link in resolution of the
142 path argument, the length of the substituted pathname string
143 exceeded {PATH_MAX}.
144 ENOENT A component of path does not name an existing file or path is an
146 empty string.
147 ENOTDIR
149 A component of the path prefix is not a directory.
150 The fpathconf() function shall fail if:
153 EINVAL The value of name is not valid.
155 The fpathconf() function may fail if:
158 EBADF The fildes argument is not a valid file descriptor.
160 EINVAL The implementation does not support an association of the vari‐
162 able name with the specified file.
163 The following sections are informative.
166
168 None.
169
171 None.
172
174 The pathconf() function was proposed immediately after the sysconf()
175 function when it was realized that some configurable values may differ
176 across file system, directory, or device boundaries.
177 For example, {NAME_MAX} frequently changes between System V and BSD-
179 based file systems; System V uses a maximum of 14, BSD 255. On an
180 implementation that provides both types of file systems, an application
181 would be forced to limit all pathname components to 14 bytes, as this
182 would be the value specified in <limits.h> on such a system.
183 Therefore, various useful values can be queried on any pathname or file
185 descriptor, assuming that the appropriate permissions are in place.
186 The value returned for the variable {PATH_MAX} indicates the longest
188 relative pathname that could be given if the specified directory is the
189 process' current working directory. A process may not always be able to
190 generate a name that long and use it if a subdirectory in the pathname
191 crosses into a more restrictive file system.
192 The value returned for the variable _POSIX_CHOWN_RESTRICTED also
194 applies to directories that do not have file systems mounted on them.
195 The value may change when crossing a mount point, so applications that
196 need to know should check for each directory. (An even easier check is
197 to try the chown() function and look for an error in case it happens.)
198 Unlike the values returned by sysconf(), the pathname-oriented vari‐
200 ables are potentially more volatile and are not guaranteed to remain
201 constant throughout the process' lifetime. For example, in between two
202 calls to pathconf(), the file system in question may have been
203 unmounted and remounted with different characteristics.
204 Also note that most of the errors are optional. If one of the variables
206 always has the same value on an implementation, the implementation need
207 not look at path or fildes to return that value and is, therefore, not
208 required to detect any of the errors except the meaning of [EINVAL]
209 that indicates that the value of name is not valid for that variable.
210 If the value of any of the limits is unspecified (logically infinite),
212 they will not be defined in <limits.h> and the pathconf() and fpath‐
213 conf() functions return -1 without changing errno. This can be distin‐
214 guished from the case of giving an unrecognized name argument because
215 errno is set to [EINVAL] in this case.
216 Since -1 is a valid return value for the pathconf() and fpathconf()
218 functions, applications should set errno to zero before calling them
219 and check errno only if the return value is -1.
220 For the case of {SYMLINK_MAX}, since both pathconf() and open() follow
222 symbolic links, there is no way that path or fildes could refer to a
223 symbolic link.
224
226 None.
227
229 confstr() , sysconf() , the Base Definitions volume of
230 IEEE Std 1003.1-2001, <limits.h>, <unistd.h>, the Shell and Utilities
231 volume of IEEE Std 1003.1-2001
232
234 Portions of this text are reprinted and reproduced in electronic form
235 from IEEE Std 1003.1, 2003 Edition, Standard for Information Technology
236 -- Portable Operating System Interface (POSIX), The Open Group Base
237 Specifications Issue 6, Copyright (C) 2001-2003 by the Institute of
238 Electrical and Electronics Engineers, Inc and The Open Group. In the
239 event of any discrepancy between this version and the original IEEE and
240 The Open Group Standard, the original IEEE and The Open Group Standard
241 is the referee document. The original Standard can be obtained online
242 at http://www.opengroup.org/unix/online.html .
243IEEE/The Open Group 2003 FPATHCONF(P)