man3/fpathconf.3

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  26 .\" Modified Wed Jul 28 11:12:26 1993 by Rik Faith (faith@cs.unc.edu)
  27 .\"
  28 .\" FIXME Probably all of the following should be documented:
  29 .\"     _PC_SYNC_IO,
  30 .\"     _PC_ASYNC_IO,
  31 .\"     _PC_PRIO_IO,
  32 .\"     _PC_SOCK_MAXBUF,
  33 .\"     _PC_FILESIZEBITS,
  34 .\"     _PC_REC_INCR_XFER_SIZE,
  35 .\"     _PC_REC_MAX_XFER_SIZE,
  36 .\"     _PC_REC_MIN_XFER_SIZE,
  37 .\"     _PC_REC_XFER_ALIGN,
  38 .\"     _PC_ALLOC_SIZE_MIN,
  39 .\"     _PC_SYMLINK_MAX,
  40 .\"     _PC_2_SYMLINKS
  41 .\"
  42 .TH FPATHCONF 3  2017-07-13 "GNU" "Linux Programmer's Manual"
  43 .SH NAME
  44 fpathconf, pathconf \- get configuration values for files
  45 .SH SYNOPSIS
  46 .nf
  47 .B #include <unistd.h>
  48 .PP
  49 .BI "long fpathconf(int " fd ", int " name );
  50 .BI "long pathconf(const char *" path ", int " name );
  51 .fi
  52 .SH DESCRIPTION
  53 .BR fpathconf ()
  54 gets a value for the configuration option
  55 .I name
  56 for the open file descriptor
  57 .IR fd .
  58 .PP
  59 .BR pathconf ()
  60 gets a value for configuration option
  61 .I name
  62 for the filename
  63 .IR path .
  64 .PP
  65 The corresponding macros defined in
  66 .I <unistd.h>
  67 are minimum values; if an application wants to take advantage of values
  68 which may change, a call to
  69 .BR fpathconf ()
  70 or
  71 .BR pathconf ()
  72 can be made, which may yield more liberal results.
  73 .PP
  74 Setting
  75 .I name
  76 equal to one of the following constants returns the following
  77 configuration options:
  78 .TP
  79 .B _PC_LINK_MAX
  80 The maximum number of links to the file.
  81 If
  82 .I fd
  83 or
  84 .I path
  85 refer to a directory, then the value applies to the whole directory.
  86 The corresponding macro is
  87 .BR _POSIX_LINK_MAX .
  88 .TP
  89 .B _PC_MAX_CANON
  90 The maximum length of a formatted input line, where
  91 .I fd
  92 or
  93 .I path
  94 must refer to a terminal.
  95 The corresponding macro is
  96 .BR _POSIX_MAX_CANON .
  97 .TP
  98 .B _PC_MAX_INPUT
  99 The maximum length of an input line, where
 100 .I fd
 101 or
 102 .I path
 103 must refer to a terminal.
 104 The corresponding macro is
 105 .BR _POSIX_MAX_INPUT .
 106 .TP
 107 .B _PC_NAME_MAX
 108 The maximum length of a filename in the directory
 109 .I path
 110 or
 111 .IR fd
 112 that the process is allowed to create.
 113 The corresponding macro is
 114 .BR _POSIX_NAME_MAX .
 115 .TP
 116 .B _PC_PATH_MAX
 117 The maximum length of a relative pathname when
 118 .I path
 119 or
 120 .I fd
 121 is the current working directory.
 122 The corresponding macro is
 123 .BR _POSIX_PATH_MAX .
 124 .TP
 125 .B _PC_PIPE_BUF
 126 The maximum number of bytes that can be written atomically to a pipe of FIFO.
 127 For
 128 .BR fpathconf (),
 129 .I fd
 130 should refer to a pipe or FIFO.
 131 For
 132 .BR fpathconf (),
 133 .I path
 134 should refer to a FIFO or a directory; in the latter case,
 135 the returned value corresponds to FIFOs created in that directory.
 136 The corresponding macro is
 137 .BR _POSIX_PIPE_BUF .
 138 .TP
 139 .B _PC_CHOWN_RESTRICTED
 140 This returns a positive value if the use of
 141 .BR chown (2)
 142 and
 143 .BR fchown (2)
 144 for changing a file's user ID is restricted to a process
 145 with appropriate privileges,
 146 and changing a file's group ID to a value other than the process's
 147 effective group ID or one of its supplementary group IDs
 148 is restricted to a process with appropriate privileges.
 149 According to POSIX.1,
 150 this variable shall always be defined with a value other than \-1.
 151 The corresponding macro is
 152 .BR _POSIX_CHOWN_RESTRICTED .
 153 .IP
 154 If
 155 .I fd
 156 or
 157 .I path
 158 refers to a directory,
 159 then the return value applies to all files in that directory.
 160 .TP
 161 .B _PC_NO_TRUNC
 162 This returns nonzero if accessing filenames longer than
 163 .B _POSIX_NAME_MAX
 164 generates an error.
 165 The corresponding macro is
 166 .BR _POSIX_NO_TRUNC .
 167 .TP
 168 .B _PC_VDISABLE
 169 This returns nonzero if special character processing can be disabled, where
 170 .I fd
 171 or
 172 .I path
 173 must refer to a terminal.
 174 .SH RETURN VALUE
 175 The return value of these functions is one of the following:
 176 .IP * 3
 177 On error, \-1 is returned and
 178 .I errno
 179 is set to indicate the cause of the error
 180 (for example,
 181 .BR EINVAL ,
 182 indicating that
 183 .I name
 184 is invalid).
 185 .IP *
 186 If
 187 .I name
 188 corresponds to a maximum or minimum limit, and that limit is indeterminate,
 189 \-1 is returned and
 190 .I errno
 191 is not changed.
 192 (To distinguish an indeterminate limit from an error, set
 193 .I errno
 194 to zero before the call, and then check whether
 195 .I errno
 196 is nonzero when \-1 is returned.)
 197 .IP *
 198 If
 199 .I name
 200 corresponds to an option,
 201 a positive value is returned if the option is supported,
 202 and \-1 is returned if the option is not supported.
 203 .IP *
 204 Otherwise,
 205 the current value of the option or limit is returned.
 206 This value will not be more restrictive than
 207 the corresponding value that was described to the application in
 208 .I <unistd.h>
 209 or
 210 .I <limits.h>
 211 when the application was compiled.
 212 .SH ERRORS
 213 .TP
 214 .B EACCES
 215 .RB ( pathconf ())
 216 Search permission is denied for one of the directories in the path prefix of
 217 .IR path .
 218 .TP
 219 .B EBADF
 220 .RB ( fpathconf ())
 221 .I fd
 222 is not a valid file descriptor.
 223 .TP
 224 .B EINVAL
 225 .I name
 226 is invalid.
 227 .TP
 228 .B EINVAL
 229 The implementation does not support an association of
 230 .I name
 231 with the specified file.
 232 .TP
 233 .B ELOOP
 234 .RB ( pathconf ())
 235 Too many symbolic links were encountered while resolving
 236 .IR path .
 237 .TP
 238 .B ENAMETOOLONG
 239 .RB ( pathconf ())
 240 .I path
 241 is too long.
 242 .TP
 243 .B ENOENT
 244 .RB ( pathconf ())
 245 A component of
 246 .I path
 247 does not exist, or
 248 .I path
 249 is an empty string.
 250 .TP
 251 .B ENOTDIR
 252 .RB ( pathconf ())
 253 A component used as a directory in
 254 .I path
 255 is not in fact a directory.
 256 .SH ATTRIBUTES
 257 For an explanation of the terms used in this section, see
 258 .BR attributes (7).
 259 .TS
 260 allbox;
 261 lbw23 lb lb
 262 l l l.
 263 Interface       Attribute       Value
 264 T{
 265 .BR fpathconf (),
 266 .BR pathconf ()
 267 T}      Thread safety   MT-Safe
 268 .TE
 269 .SH CONFORMING TO
 270 POSIX.1-2001, POSIX.1-2008.
 271 .SH NOTES
 272 Files with name lengths longer than the value returned for
 273 .I name
 274 equal to
 275 .B _PC_NAME_MAX
 276 may exist in the given directory.
 277 .PP
 278 Some returned values may be huge; they are not suitable for allocating
 279 memory.
 280 .SH SEE ALSO
 281 .BR getconf (1),
 282 .BR open (2),
 283 .BR statfs (2),
 284 .BR confstr (3),
 285 .BR sysconf (3)