In normal (i.e., nonfilesystem) resource managers, the io_devctl() function is used
to implement device control functions.
We used this in the ADIOS data acquisition driver to, for example, get the configuration of the
device.
In a filesystem resource manager, io_devctl() is used to get various information about
the filesystem.
A large number of the commands aren't used for anything other than block I/O filesystems; a few are reserved for internal use only.
Here's a summary of the commands:
- DCMD_BLK_PARTENTRY
- Used by x86 disk partitions with harddisk-based filesystems.
- DCMD_BLK_PART_DESCRIPTION
- Get extended partition description details.
- DCMD_BLK_FORCE_RELEARN
- Triggers a media reversioning and cache invalidation (for removable media).
This command is also used to sync-up the filesystem if utilities play with it “behind its back.”
- DCMD_FSYS_STATISTICS and DCMD_FSYS_STATISTICS_CLR
- Returns struct fs_stats (see <sys/fs_stats.h>).
The “_CLR” version resets the counters to zero after returning their values.
The
fsysinfo
utility is a front end for DCMD_FSYS_STATISTICS.
- DCMD_FSYS_STATVFS
- Returns struct __msg_statvfs (see below for more details).
- DCMD_FSYS_MOUNTED_ON, DCMD_FSYS_MOUNTED_AT and DCMD_FSYS_MOUNTED_BY
- Each returns 256 bytes of character data, giving information about their relationship to other filesystems.
See the discussion below.
- DCMD_FSYS_OPTIONS
- Returns 256 bytes of character data.
This can be used to return the command-line options that the filesystem was mounted with.