PATHCONF(2) System Calls Manual PATHCONF(2)

fpathconf, pathconfget configurable pathname variables

#include <unistd.h>

fpathconf(int fildes, int name);

pathconf(const char *path, int name);

The () and () functions provides a method for applications to determine the current value of a configurable system limit or option variable associated with a pathname or file descriptor.

For pathconf, the path argument is the name of a file or directory. For fpathconf, the fildes argument is an open file descriptor. The name argument specifies the system variable to be queried. Symbolic constants for each name value are found in the include file <unistd.h>.

The available values are as follows:

The maximum file link count.
The maximum number of bytes in terminal canonical input line.
The minimum maximum number of bytes for which space is available in a terminal input queue.
The maximum number of bytes in a file name.
The maximum number of bytes in a pathname.
The maximum number of bytes which will be written atomically to a pipe.
Return 1 if appropriate privileges are required for the chown(2) system call, otherwise 0.
Return 1 if file names longer than KERN_NAME_MAX are truncated.
Returns the terminal character disabling value.
The minimum number of bits needed to represent, as a signed integer value, the maximum size of a regular file allowed in the specified directory. The max file size is 2^(_PC_FILESIZEBITS - 1).
Returns the number of bits used to store maximum extended attribute size in bytes. For example, if the maximum attribute size supported by a file system is 128K, the value returned will be 18. However a value 18 can mean that the maximum attribute size can be anywhere from (256KB - 1) to 128KB. As a special case, the resource fork can have much larger size, and some file system specific extended attributes can have smaller and preset size; for example, Finder Info is always 32 bytes.
If a file system supports the reporting of holes (see lseek(2)), () and () return a positive number that represents the minimum hole size returned in bytes. The offsets of holes returned will be aligned to this same value. A special value of 1 is returned if the file system does not specify the minimum hole size but still reports holes.

If the call to pathconf or fpathconf is not successful, -1 is returned and errno is set appropriately. Otherwise, if the variable is associated with functionality that does not have a limit in the system, -1 is returned and errno is not modified. Otherwise, the current variable value is returned.

If any of the following conditions occur, the pathconf and fpathconf functions shall return -1 and set errno to the corresponding value.

The value of the name argument is invalid.
The implementation does not support an association of the variable name with the associated file.

pathconf() will fail if:

Search permission is denied for a component of the path prefix.
An I/O error occurs while reading from or writing to the file system.
Too many symbolic links are encountered in translating the pathname. This is taken to be indicative of a looping symbolic link.
A component of a pathname exceeded 255 characters, or an entire path name exceeded 1023 characters.
The named file does not exist.
A component of the path prefix is not a directory.

fpathconf() will fail if:

fildes is not a valid open file descriptor.
An I/O error occurs while reading from or writing to the file system.


The pathconf and fpathconf functions first appeared in 4.4BSD.

June 4, 1993 BSD 4