fpathconf, pathconf - get configuration values for files

#include <unistd.h>
long fpathconf(int fd, int name);
long pathconf(const char *path, int name);

fpathconf() gets a value for the configuration option name for the open file descriptor fd.

pathconf() gets a value for configuration option name for the filename path.

The corresponding macros defined in <unistd.h> are minimum values; if an application wants to take advantage of values which may change, a call to fpathconf() or pathconf() can be made, which may yield more liberal results.

Setting name equal to one of the following constants returns the following configuration options:

_PC_LINK_MAX

The maximum number of links to the file. If fd or path refer to a directory, then the value applies to the whole directory. The corresponding macro is _POSIX_LINK_MAX.

_PC_MAX_CANON

The maximum length of a formatted input line, where fd or path must refer to a terminal. The corresponding macro is _POSIX_MAX_CANON.

_PC_MAX_INPUT

The maximum length of an input line, where fd or path must refer to a terminal. The corresponding macro is _POSIX_MAX_INPUT.

_PC_NAME_MAX

The maximum length of a filename in the directory path or fd that the process is allowed to create. The corresponding macro is _POSIX_NAME_MAX.

_PC_PATH_MAX

The maximum length of a relative pathname when path or fd is the current working directory. The corresponding macro is _POSIX_PATH_MAX.

_PC_PIPE_BUF

The maximum number of bytes that can be written atomically to a pipe of FIFO. For fpathconf(), fd should refer to a pipe or FIFO. For fpathconf(), path should refer to a FIFO or a directory; in the latter case, the returned value corresponds to FIFOs created in that directory. The corresponding macro is _POSIX_PIPE_BUF.

_PC_CHOWN_RESTRICTED

This returns a positive value if the use of chown(2) and fchown(2) for changing a file's user ID is restricted to a process with appropriate privileges, and changing a file's group ID to a value other than the process's effective group ID or one of its supplementary group IDs is restricted to a process with appropriate privileges. According to POSIX.1, this variable shall always be defined with a value other than -1. The corresponding macro is _POSIX_CHOWN_RESTRICTED.

If fd or path refers to a directory, then the return value applies to all files in that directory.

_PC_NO_TRUNC

This returns nonzero if accessing filenames longer than _POSIX_NAME_MAX generates an error. The corresponding macro is _POSIX_NO_TRUNC.

_PC_VDISABLE

This returns nonzero if special character processing can be disabled, where fd or path must refer to a terminal.

The return value of these functions is one of the following:

• On error, -1 is returned and errno is set to indicate the error (for example, EINVAL, indicating that name is invalid).

• If name corresponds to a maximum or minimum limit, and that limit is indeterminate, -1 is returned and errno is not changed. (To distinguish an indeterminate limit from an error, set errno to zero before the call, and then check whether errno is nonzero when -1 is returned.)

• If name corresponds to an option, a positive value is returned if the option is supported, and -1 is returned if the option is not supported.

• Otherwise, the current value of the option or limit is returned. This value will not be more restrictive than the corresponding value that was described to the application in <unistd.h> or <limits.h> when the application was compiled.

getconf(1), open(2), statfs(2), confstr(3), sysconf(3)