Get filesystem information, given a file descriptor
Synopsis:
#include <sys/statvfs.h>
int fstatvfs( int fildes,
struct statvfs *buf );
int fstatvfs64( int fildes,
struct statvfs64 *buf );
Arguments:
- fildes
- 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:
In QNX Neutrino 6.6 or later, 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 fildes 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 nonsuperuser.
- 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 nonsuperuser.
- 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. |
- 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,
fs-etfs-ram
- These filesystems have a fixed inodes table, so they fill in these fields.
- fs-mac.so,
fs-nt.so,
fs-udf.so
- Read-only fsystems always set f_ffree and f_favail to 0.
Where possible or known, they try to set f_files:
- fs-mac.so knows exactly
- fs-nt.so provides an upper bound based on the current size
of the Master File Table (MFT)
- fs-udf.so knows when it's a UDF that's mounted;
ISO formats don't indicate that information, so f_files is set to 0
- fs-cifs
- The CIFS filesystem sets these fields 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 fildes 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 |
| Interrupt handler |
No |
| Signal handler |
Yes |
| Thread |
Yes |