1FPATHCONF(3P) POSIX Programmer's Manual FPATHCONF(3P)
2
6 This manual page is part of the POSIX Programmer's Manual. The Linux
7 implementation of this interface may differ (consult the corresponding
8 Linux manual page for details of Linux behavior), or the interface may
9 not be implemented on Linux.
10
12 fpathconf, pathconf - get configurable pathname variables
13
15 #include <unistd.h>
16 long fpathconf(int fildes, int name);
18 long pathconf(const char *path, int name);
19
22 The fpathconf() and pathconf() functions shall determine the current
23 value of a configurable limit or option (variable) that is associated
24 with a file or directory.
25 For pathconf(), the path argument points to the pathname of a file or
27 directory.
28 For fpathconf(), the fildes argument is an open file descriptor.
30 The name argument represents the variable to be queried relative to
32 that file or directory. Implementations shall support all of the vari‐
33 ables listed in the following table and may support others. The vari‐
34 ables in the following table come from <limits.h> or <unistd.h> and the
35 symbolic constants, defined in <unistd.h>, are the corresponding values
36 used for name.
37 Variable Value of name Requirements
39 {FILESIZEBITS} _PC_FILESIZEBITS 3,4
40 {LINK_MAX} _PC_LINK_MAX 1
41 {MAX_CANON} _PC_MAX_CANON 2
42 {MAX_INPUT} _PC_MAX_INPUT 2
43 {NAME_MAX} _PC_NAME_MAX 3,4
44 {PATH_MAX} _PC_PATH_MAX 4,5
45 {PIPE_BUF} _PC_PIPE_BUF 6
46 {POSIX_ALLOC_SIZE_MIN} _PC_ALLOC_SIZE_MIN
47 {POSIX_REC_INCR_XFER_SIZE} _PC_REC_INCR_XFER_SIZE
48 {POSIX_REC_MAX_XFER_SIZE} _PC_REC_MAX_XFER_SIZE
49 {POSIX_REC_MIN_XFER_SIZE} _PC_REC_MIN_XFER_SIZE
50 {POSIX_REC_XFER_ALIGN} _PC_REC_XFER_ALIGN
51 {SYMLINK_MAX} _PC_SYMLINK_MAX 4,9
52 _POSIX_CHOWN_RESTRICTED _PC_CHOWN_RESTRICTED 7
53 _POSIX_NO_TRUNC _PC_NO_TRUNC 3,4
54 _POSIX_VDISABLE _PC_VDISABLE 2
55 _POSIX_ASYNC_IO _PC_ASYNC_IO 8
56 _POSIX_PRIO_IO _PC_PRIO_IO 8
57 _POSIX_SYNC_IO _PC_SYNC_IO 8
58 Requirements
60 1. If path or fildes refers to a directory, the value returned shall
61 apply to the directory itself.
62 2. If path or fildes does not refer to a terminal file, it is unspeci‐
64 fied whether an implementation supports an association of the vari‐
65 able name with the specified file.
66 3. If path or fildes refers to a directory, the value returned shall
68 apply to filenames within the directory.
69 4. If path or fildes does not refer to a directory, it is unspecified
71 whether an implementation supports an association of the variable
72 name with the specified file.
73 5. If path or fildes refers to a directory, the value returned shall
75 be the maximum length of a relative pathname when the specified
76 directory is the working directory.
77 6. If path refers to a FIFO, or fildes refers to a pipe or FIFO, the
79 value returned shall apply to the referenced object. If path or
80 fildes refers to a directory, the value returned shall apply to any
81 FIFO that exists or can be created within the directory. If path or
82 fildes refers to any other type of file, it is unspecified whether
83 an implementation supports an association of the variable name with
84 the specified file.
85 7. If path or fildes refers to a directory, the value returned shall
87 apply to any files, other than directories, that exist or can be
88 created within the directory.
89 8. If path or fildes refers to a directory, it is unspecified whether
91 an implementation supports an association of the variable name with
92 the specified file.
93 9. If path or fildes refers to a directory, the value returned shall
95 be the maximum length of the string that a symbolic link in that
96 directory can contain.
97
99 If name is an invalid value, both pathconf() and fpathconf() shall
100 return -1 and set errno to indicate the error.
101 If the variable corresponding to name has no limit for the path or file
103 descriptor, both pathconf() and fpathconf() shall return -1 without
104 changing errno. If the implementation needs to use path to determine
105 the value of name and the implementation does not support the associa‐
106 tion of name with the file specified by path, or if the process did not
107 have appropriate privileges to query the file specified by path, or
108 path does not exist, pathconf() shall return -1 and set errno to indi‐
109 cate the error.
110 If the implementation needs to use fildes to determine the value of
112 name and the implementation does not support the association of name
113 with the file specified by fildes, or if fildes is an invalid file
114 descriptor, fpathconf() shall return -1 and set errno to indicate the
115 error.
116 Otherwise, pathconf() or fpathconf() shall return the current variable
118 value for the file or directory without changing errno. The value
119 returned shall not be more restrictive than the corresponding value
120 available to the application when it was compiled with the implementa‐
121 tion's <limits.h> or <unistd.h>.
122
124 The pathconf() function shall fail if:
125 EINVAL The value of name is not valid.
127 ELOOP A loop exists in symbolic links encountered during resolution of
129 the path argument.
130 The pathconf() function may fail if:
133 EACCES Search permission is denied for a component of the path prefix.
135 EINVAL The implementation does not support an association of the vari‐
137 able name with the specified file.
138 ELOOP More than {SYMLOOP_MAX} symbolic links were encountered during
140 resolution of the path argument.
141 ENAMETOOLONG
143 The length of the path argument exceeds {PATH_MAX} or a pathname
144 component is longer than {NAME_MAX}.
145 ENAMETOOLONG
147 As a result of encountering a symbolic link in resolution of the
148 path argument, the length of the substituted pathname string
149 exceeded {PATH_MAX}.
150 ENOENT A component of path does not name an existing file or path is an
152 empty string.
153 ENOTDIR
155 A component of the path prefix is not a directory.
156 The fpathconf() function shall fail if:
159 EINVAL The value of name is not valid.
161 The fpathconf() function may fail if:
164 EBADF The fildes argument is not a valid file descriptor.
166 EINVAL The implementation does not support an association of the vari‐
168 able name with the specified file.
169 The following sections are informative.
172
174 None.
175
177 None.
178
180 The pathconf() function was proposed immediately after the sysconf()
181 function when it was realized that some configurable values may differ
182 across file system, directory, or device boundaries.
183 For example, {NAME_MAX} frequently changes between System V and BSD-
185 based file systems; System V uses a maximum of 14, BSD 255. On an
186 implementation that provides both types of file systems, an application
187 would be forced to limit all pathname components to 14 bytes, as this
188 would be the value specified in <limits.h> on such a system.
189 Therefore, various useful values can be queried on any pathname or file
191 descriptor, assuming that the appropriate permissions are in place.
192 The value returned for the variable {PATH_MAX} indicates the longest
194 relative pathname that could be given if the specified directory is the
195 process' current working directory. A process may not always be able to
196 generate a name that long and use it if a subdirectory in the pathname
197 crosses into a more restrictive file system.
198 The value returned for the variable _POSIX_CHOWN_RESTRICTED also
200 applies to directories that do not have file systems mounted on them.
201 The value may change when crossing a mount point, so applications that
202 need to know should check for each directory. (An even easier check is
203 to try the chown() function and look for an error in case it happens.)
204 Unlike the values returned by sysconf(), the pathname-oriented vari‐
206 ables are potentially more volatile and are not guaranteed to remain
207 constant throughout the process' lifetime. For example, in between two
208 calls to pathconf(), the file system in question may have been
209 unmounted and remounted with different characteristics.
210 Also note that most of the errors are optional. If one of the variables
212 always has the same value on an implementation, the implementation need
213 not look at path or fildes to return that value and is, therefore, not
214 required to detect any of the errors except the meaning of [EINVAL]
215 that indicates that the value of name is not valid for that variable.
216 If the value of any of the limits is unspecified (logically infinite),
218 they will not be defined in <limits.h> and the pathconf() and fpath‐
219 conf() functions return -1 without changing errno. This can be distin‐
220 guished from the case of giving an unrecognized name argument because
221 errno is set to [EINVAL] in this case.
222 Since -1 is a valid return value for the pathconf() and fpathconf()
224 functions, applications should set errno to zero before calling them
225 and check errno only if the return value is -1.
226 For the case of {SYMLINK_MAX}, since both pathconf() and open() follow
228 symbolic links, there is no way that path or fildes could refer to a
229 symbolic link.
230
232 None.
233
235 confstr(), sysconf(), the Base Definitions volume of
236 IEEE Std 1003.1-2001, <limits.h>, <unistd.h>, the Shell and Utilities
237 volume of IEEE Std 1003.1-2001
238
240 Portions of this text are reprinted and reproduced in electronic form
241 from IEEE Std 1003.1, 2003 Edition, Standard for Information Technology
242 -- Portable Operating System Interface (POSIX), The Open Group Base
243 Specifications Issue 6, Copyright (C) 2001-2003 by the Institute of
244 Electrical and Electronics Engineers, Inc and The Open Group. In the
245 event of any discrepancy between this version and the original IEEE and
246 The Open Group Standard, the original IEEE and The Open Group Standard
247 is the referee document. The original Standard can be obtained online
248 at http://www.opengroup.org/unix/online.html .
249IEEE/The Open Group 2003 FPATHCONF(3P)