fstatvfs(), fstatvfs64()

QNX SDP8.0C Library ReferenceAPIDeveloper

Get filesystem information, given a file descriptor

Synopsis:

#include <sys/statvfs.h>

int fstatvfs( int filedes, 
              struct statvfs *buf );

int fstatvfs64( int filedes,
                struct statvfs64 *buf );

Arguments:

filedes: The descriptor for a file that resides on the filesystem that you want to get information about.
buf: A pointer to a buffer where the function can store information about the filesystem; see below.

Library:

libc

Use the -l c option to qcc to link against this library. This library is usually included automatically.

Description:

The fstatvfs() and fstatvfs64() functions return a generic superblock describing a filesystem that you can use to get information about mounted filesystems. The fstatvfs64() function is a large-file support version of fstatvfs(). The statvfs() and statvfs64() functions are similar, but they take a path name instead of a file descriptor.

Note:

The large-file support functions and data types appear in the name space only if you define _LARGEFILE64_SOURCE when you compile your code. For more information, see Classification in What's in a Function Description?

The filedes argument is an open file descriptor, obtained from a successful call to open(), creat(), dup(), fcntl(), or pipe(), for a file that resides on that filesystem. The filesystem type is known to the operating system. Read, write, or execute permission for the named file isn't required.

The buf argument is a pointer to a statvfs or statvfs64 structure that's filled by the function. It contains at least:

unsigned long f_bsize: The preferred filesystem blocksize.
unsigned long f_frsize: The fundamental filesystem blocksize (if supported).
fsblkcnt_t f_blocks: The total number of blocks on the filesystem, in units of f_frsize.
fsblkcnt_t f_bfree: The total number of free blocks.
fsblkcnt_t f_bavail: The number of free blocks available to a non-privileged process.

Note:

Many file systems do not have a concept of "privileged user". For those file systems, f_bavail will equal f_bfree, and f_favail will equal f_ffree.

fsfilcnt_t f_files

The total number of file nodes (inodes).

fsfilcnt_t f_ffree

The total number of free file nodes.

fsfilcnt_t f_favail

The number of inodes available to a non-privileged process.

unsigned long f_fsid

The filesystem ID (currently the device ID).

char f_basetype[16]

The type of the target filesystem, as a null-terminated string.

unsigned long f_flag

A bitmask of flags; the function can set these flags (the _MOUNT_* and ST_* bits are equivalent):


_MOUNT_*	ST_*	Meaning
_MOUNT_READONLY	ST_RDONLY	The filesystem is read-only.
_MOUNT_NOEXEC	ST_NOEXEC	The filesystem doesn't permit the loading of executables.
_MOUNT_NOSUID	ST_NOSUID	The filesystem doesn't support setuid() and setgid() semantics.
_MOUNT_NOCREAT	ST_NOCREAT	You can't create files on the filesystem.
_MOUNT_OFF32	ST_OFF32	The off_t type is limited to 32 bits.
_MOUNT_NOATIME	ST_NOATIME	The filesystem doesn't support the logging of file access times.
_MOUNT_TRUSTED	ST_TRUSTED	The filesystem is trusted.

unsigned long f_namemax

The maximum filename length.

The values returned for f_files, f_ffree, and f_favail depend on the filesystem:

fs-dos.so: This filesystem embeds inodes in directories, so the number of files is limited by the amount of disk space, so basically there's no limit. It doesn't count the number of files created either, so it sets all these fields to 0.
fs-qnx6.so: This filesystem has a fixed inodes table, so it fills in these fields.
fs-udf.so: This read-only filesystem always sets f_ffree and f_favail to 0. For fs-udf.so, it knows when a UDF is mounted—ISO formats don't indicate that information—so f_files is set to 0.
devf-*: Flash filesystem drivers estimate the values of these fields, based on the amount of free space.

The underlying resource managers provide this information via the DCMD_FSYS_STATVFS devctl() command.

Returns:

0: Success.
-1: An error occurred (errno is set).

Errors:

EBADF: The filedes argument isn't an open file descriptor.
EFAULT: The buf argument points to an illegal address.
EINTR: A signal was caught during execution.
EIO: An I/O error occurred while reading the filesystem.
EOVERFLOW: One of the values to be returned can't be represented correctly in the structure pointed to by buf.

Classification:

fstatvfs() is POSIX 1003.1; fstatvfs64() is Large-file support


Safety:
Cancellation point	No
Signal handler	Yes
Thread	Yes

Page updated: August 09, 2024