pathconf

Name

pathconf, fpathconf
- get configurable pathname variables

Library

libc.lib

Synopsis

#include <unistd.h>

long pathconf (const char *path, int name);

long fpathconf (int fd, int name);

Return values

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.

Detailed description

The pathconf and fpathconf system calls provide 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 fd 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:

_PC_LINK_MAX
	The maximum file link count.
_PC_MAX_CANON
	The maximum number of bytes in terminal canonical input line.
_PC_MAX_INPUT
	The minimum maximum number of bytes for which space is available in a terminal input queue.
_PC_NAME_MAX
	The maximum number of bytes in a file name.
_PC_PATH_MAX
	The maximum number of bytes in a pathname.
_PC_PIPE_BUF
	The maximum number of bytes which will be written atomically to a pipe.
_PC_CHOWN_RESTRICTED
	Return 1 if appropriate privilege is required for the chown system call, otherwise 0. -p1003.1-2001 requires appropriate privilege in all cases, but this behavior was optional in prior editions of the standard.
_PC_NO_TRUNC
	Return greater than zero if attempts to use pathname components longer than .Brq Dv NAME_MAX will result in an [`ENAMETOOLONG`] error; otherwise, such components will be truncated to .Brq Dv NAME_MAX. -p1003.1-2001 requires the error in all cases, but this behavior was optional in prior editions of the standard, and some non- POSIX -compliant file systems do not support this behavior.
_PC_VDISABLE
	Returns the terminal character disabling value.
_PC_ASYNC_IO
	Return 1 if asynchronous I/O is supported, otherwise 0.
_PC_PRIO_IO
	Returns 1 if prioritised I/O is supported for this file, otherwise 0.
_PC_SYNC_IO
	Returns 1 if synchronised I/O is supported for this file, otherwise 0.
_PC_ALLOC_SIZE_MIN
	Minimum number of bytes of storage allocated for any portion of a file.
_PC_FILESIZEBITS
	Number of bits needed to represent the maximum file size.
_PC_REC_INCR_XFER_SIZE
	Recommended increment for file transfer sizes between `_PC_REC_MIN_XFER_SIZE` and `_PC_REC_MAX_XFER_SIZE.`
_PC_REC_MAX_XFER_SIZE
	Maximum recommended file transfer size.
_PC_REC_MIN_XFER_SIZE
	Minimum recommended file transfer size.
_PC_REC_XFER_ALIGN
	Recommended file transfer buffer alignment.
_PC_SYMLINK_MAX
	Maximum number of bytes in a symbolic link.
_PC_ACL_EXTENDED
	Returns 1 if an Access Control List (ACL) can be set on the specified file, otherwise 0.
_PC_ACL_PATH_MAX
	Maximum number of ACL entries per file.
_PC_CAP_PRESENT
	Returns 1 if a capability state can be set on the specified file, otherwise 0.
_PC_INF_PRESENT
	Returns 1 if an information label can be set on the specified file, otherwise 0.
_PC_MAC_PRESENT
	Returns 1 if a Mandatory Access Control (MAC) label can be set on the specified file, otherwise 0.

Examples

#include<unistd.h>
#include<stdio.h>
int test_pathconf()
{
   int fp = open("test_pathconf1.txt", O_RDWR|O_CREAT);
   if(fp != -1)
   {
     int n = pathconf("test_pathconf1.txt", _PC_LINK_MAX);
     if( n < _POSIX_LINK_MAX )
     {
       return -1;
     }
     else
     {
       printf("_PC_LINK_MAX value: %d", n);
       printf("Pathconf passed");
       return 0;
     }
   }
   else
   {
     printf("failed");
     return -1;
   }    
}

Output

_PC_LINK_MAX value: 1
Pathconf passed

Errors

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

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

The pathconf system call will fail if:

[`ENOTDIR`]
	A component of the path prefix is not a directory.
[`ENAMETOOLONG`]
	A component of a pathname exceeded .Brq Dv NAME_MAX characters (but see `_PC_NO_TRUNC` above), or an entire path name exceeded .Brq Dv PATH_MAX characters.
[`ENOENT`]
	The named file does not exist.
[`EACCES`]
	Search permission is denied for a component of the path prefix.
[`ELOOP`]
	Too many symbolic links were encountered in translating the pathname.
[`EIO`]	An I/O error occurred while reading from or writing to the file system.

The fpathconf system call will fail if:

[`EBADF`]
	The fd argument is not a valid open file descriptor.
[`EIO`]	An I/O error occurred while reading from or writing to the file system.

Note

The current implementation of the functions pathconf and fpathconf considers only the following configurable variables.

_PC_LINK_MAX _PC_MAX_CANON _PC_MAX_INPUT _PC_NAME_MAX _PC_PATH_MAX _PC_PIPE_BUF _PC_CHOWN_RESTRICTED _PC_NO_TRUNC _PC_VDISABLE
	Also, these functions return the limits as required by the POSIX standard instead of the actual system limits determined on the run.

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