QNX 4 compatible filesystem support
driver ... qnx4 qnx4_options... &
Where driver is any of the devb-* drivers, and qnx4_options is one or more of the following, separated by commas:
- When to pre-read the .bitmap file.
Scanning the bitmap is required to return the count of free blocks.
It also allows for improved
performance by creating an in-memory summary of
where free blocks might be located within the filesystem.
The value must be one of the following:
- always — calculate/store .bitmap details for all media.
- lazy — don't read the bitmap for non-removable media at mount time, but when it's first needed (e.g. by a statvfs() call or df). This can help speed up system boot times (since on a large disk, the .bitmap files may be several megabytes in length, and if read right away, can interfere with the starting of other processes on an embedded system).
- nonrmv (the default) — act as always for nonremovable media, and lazy for removable media
- Allow persistent over-grown files; don't truncate them when they're closed. Certain file-write access patterns (e.g O_APPEND) are detected, and the file isn't shrunk back at the last close. This is useful for log files that you keep appending to, and so on.
- Never embed inode details; always place in fixed-size .inodes.
- Enable a more aggressive file-extent over-allocation heuristic.
- Attempt to repair any file marked as “busy” on the filesystem (i.e. a file that was being grown or shrunk when the system was improperly shutdown). The default action is to return EBADFSYS to any attempt to open such a file; this option will instead truncate the file to its last-known valid size, unset the “busy” indicator, and allow access. This truncation may result in lost data and unused blocks marked as used in the bitmap, so run chkfsys later to ensure full filesystem consistency.
The fs-qnx4.so shared object provides support for QNX 4 filesystems. It's automatically loaded by the devb-* drivers when mounting a QNX 4 filesystem.
- To enable support for long filenames (more than 48 characters) on an
existing QNX 4 compatible filesystem, login as root and
create an empty, read-only file named .longfilenames in
the root directory of that filesystem.
To enable support for long filenames on a new QNX 4 filesystem, use the -N option to dinit.
Filesystems chapter of System Architecture
QNX Neutrino User's Guide:
- “QNX 4 filesystem” in the Working With Filesystems chapter
- “Filesystems and block I/O (devb-*) drivers” in the Fine-Tuning Your System chapter
- “Filesystem limits” in the Understanding System Limits chapter