Originální popis anglicky:
fpathconf, pathconf - get configurable pathname variables
Návod, kniha: POSIX Programmer's Manual
#include <unistd.h>
long fpathconf(int
fildes, int
name);
long pathconf(const char *
path, int
name );
The
fpathconf() and
pathconf() functions shall determine the
current value of a configurable limit or option (
variable) that is
associated with a file or directory.
For
pathconf(), the
path argument points to the pathname of a file
or directory.
For
fpathconf(), the
fildes argument is an open file descriptor.
The
name argument represents the variable to be queried relative to that
file or directory. Implementations shall support all of the variables listed
in the following table and may support others. The variables in the following
table come from
<limits.h> or
<unistd.h> and the
symbolic constants, defined in
<unistd.h>, are the corresponding
values used for
name.
| Variable |
Value of name |
Requirements |
| {FILESIZEBITS} |
_PC_FILESIZEBITS |
3,4 |
| {LINK_MAX} |
_PC_LINK_MAX |
1 |
| {MAX_CANON} |
_PC_MAX_CANON |
2 |
| {MAX_INPUT} |
_PC_MAX_INPUT |
2 |
| {NAME_MAX} |
_PC_NAME_MAX |
3,4 |
| {PATH_MAX} |
_PC_PATH_MAX |
4,5 |
| {PIPE_BUF} |
_PC_PIPE_BUF |
6 |
| {POSIX_ALLOC_SIZE_MIN} |
_PC_ALLOC_SIZE_MIN |
|
| {POSIX_REC_INCR_XFER_SIZE} |
_PC_REC_INCR_XFER_SIZE |
|
| {POSIX_REC_MAX_XFER_SIZE} |
_PC_REC_MAX_XFER_SIZE |
|
| {POSIX_REC_MIN_XFER_SIZE} |
_PC_REC_MIN_XFER_SIZE |
|
| {POSIX_REC_XFER_ALIGN} |
_PC_REC_XFER_ALIGN |
|
| {SYMLINK_MAX} |
_PC_SYMLINK_MAX |
4,9 |
| _POSIX_CHOWN_RESTRICTED |
_PC_CHOWN_RESTRICTED |
7 |
| _POSIX_NO_TRUNC |
_PC_NO_TRUNC |
3,4 |
| _POSIX_VDISABLE |
_PC_VDISABLE |
2 |
| _POSIX_ASYNC_IO |
_PC_ASYNC_IO |
8 |
| _POSIX_PRIO_IO |
_PC_PRIO_IO |
8 |
| _POSIX_SYNC_IO |
_PC_SYNC_IO |
8 |
- 1.
- If path or fildes refers to a directory, the
value returned shall apply to the directory itself.
- 2.
- If path or fildes does not refer to a
terminal file, it is unspecified whether an implementation supports an
association of the variable name with the specified file.
- 3.
- If path or fildes refers to a directory, the
value returned shall apply to filenames within the directory.
- 4.
- If path or fildes does not refer to a
directory, it is unspecified whether an implementation supports an
association of the variable name with the specified file.
- 5.
- If path or fildes refers to a directory, the
value returned shall be the maximum length of a relative pathname when the
specified directory is the working directory.
- 6.
- If path refers to a FIFO, or fildes refers to
a pipe or FIFO, the value returned shall apply to the referenced object.
If path or fildes refers to a directory, the value returned
shall apply to any FIFO that exists or can be created within the
directory. If path or fildes refers to any other type of
file, it is unspecified whether an implementation supports an association
of the variable name with the specified file.
- 7.
- If path or fildes refers to a directory, the
value returned shall apply to any files, other than directories, that
exist or can be created within the directory.
- 8.
- If path or fildes refers to a directory, it
is unspecified whether an implementation supports an association of the
variable name with the specified file.
- 9.
- If path or fildes refers to a directory, the
value returned shall be the maximum length of the string that a symbolic
link in that directory can contain.
If
name is an invalid value, both
pathconf() and
fpathconf() shall return -1 and set
errno to indicate the error.
If the variable corresponding to
name has no limit for the
path or
file descriptor, both
pathconf() and
fpathconf() shall return -1
without changing
errno. If the implementation needs to use
path
to determine the value of
name and the implementation does not support
the association of
name with the file specified by
path, or if
the process did not have appropriate privileges to query the file specified by
path, or
path does not exist,
pathconf() shall return -1
and set
errno to indicate the error.
If the implementation needs to use
fildes to determine the value of
name and the implementation does not support the association of
name with the file specified by
fildes, or if
fildes is
an invalid file descriptor,
fpathconf() shall return -1 and set
errno to indicate the error.
Otherwise,
pathconf() or
fpathconf() shall return the current
variable value for the file or directory without changing
errno. The
value returned shall not be more restrictive than the corresponding value
available to the application when it was compiled with the implementation's
<limits.h> or
<unistd.h>.
The
pathconf() function shall fail if:
- EINVAL
- The value of name is not valid.
- ELOOP
- A loop exists in symbolic links encountered during
resolution of the path argument.
The
pathconf() function may fail if:
- EACCES
- Search permission is denied for a component of the path
prefix.
- EINVAL
- The implementation does not support an association of the
variable name with the specified file.
- ELOOP
- More than {SYMLOOP_MAX} symbolic links were encountered
during resolution of the path argument.
- ENAMETOOLONG
- The length of the path argument exceeds {PATH_MAX}
or a pathname component is longer than {NAME_MAX}.
- ENAMETOOLONG
- As a result of encountering a symbolic link in resolution
of the path argument, the length of the substituted pathname string
exceeded {PATH_MAX}.
- ENOENT
- A component of path does not name an existing file
or path is an empty string.
- ENOTDIR
- A component of the path prefix is not a directory.
The
fpathconf() function shall fail if:
- EINVAL
- The value of name is not valid.
The
fpathconf() function may fail if:
- EBADF
- The fildes argument is not a valid file
descriptor.
- EINVAL
- The implementation does not support an association of the
variable name with the specified file.
The following sections are informative.
None.
None.
The
pathconf() function was proposed immediately after the
sysconf() function when it was realized that some configurable values
may differ across file system, directory, or device boundaries.
For example, {NAME_MAX} frequently changes between System V and BSD-based file
systems; System V uses a maximum of 14, BSD 255. On an implementation that
provides both types of file systems, an application would be forced to limit
all pathname components to 14 bytes, as this would be the value specified in
<limits.h> on such a system.
Therefore, various useful values can be queried on any pathname or file
descriptor, assuming that the appropriate permissions are in place.
The value returned for the variable {PATH_MAX} indicates the longest relative
pathname that could be given if the specified directory is the process'
current working directory. A process may not always be able to generate a name
that long and use it if a subdirectory in the pathname crosses into a more
restrictive file system.
The value returned for the variable _POSIX_CHOWN_RESTRICTED also applies to
directories that do not have file systems mounted on them. The value may
change when crossing a mount point, so applications that need to know should
check for each directory. (An even easier check is to try the
chown()
function and look for an error in case it happens.)
Unlike the values returned by
sysconf(), the pathname-oriented variables
are potentially more volatile and are not guaranteed to remain constant
throughout the process' lifetime. For example, in between two calls to
pathconf(), the file system in question may have been unmounted and
remounted with different characteristics.
Also note that most of the errors are optional. If one of the variables always
has the same value on an implementation, the implementation need not look at
path or
fildes to return that value and is, therefore, not
required to detect any of the errors except the meaning of [EINVAL] that
indicates that the value of
name is not valid for that variable.
If the value of any of the limits is unspecified (logically infinite), they will
not be defined in
<limits.h> and the
pathconf() and
fpathconf() functions return -1 without changing
errno. This can
be distinguished from the case of giving an unrecognized
name argument
because
errno is set to [EINVAL] in this case.
Since -1 is a valid return value for the
pathconf() and
fpathconf() functions, applications should set
errno to zero
before calling them and check
errno only if the return value is -1.
For the case of {SYMLINK_MAX}, since both
pathconf() and
open()
follow symbolic links, there is no way that
path or
fildes could
refer to a symbolic link.
None.
confstr() ,
sysconf() , the Base Definitions volume of
IEEE Std 1003.1-2001,
<limits.h>,
<unistd.h>, the Shell and Utilities volume of
IEEE Std 1003.1-2001
Portions of this text are reprinted and reproduced in electronic form from IEEE
Std 1003.1, 2003 Edition, Standard for Information Technology -- Portable
Operating System Interface (POSIX), The Open Group Base Specifications Issue
6, Copyright (C) 2001-2003 by the Institute of Electrical and Electronics
Engineers, Inc and The Open Group. In the event of any discrepancy between
this version and the original IEEE and The Open Group Standard, the original
IEEE and The Open Group Standard is the referee document. The original
Standard can be obtained online at http://www.opengroup.org/unix/online.html
.
