These options control the formatting of an MMFS disk. They are only
used when a filesystem is formatted. Under normal circumstances the
filesystem will fetch these values from the disk volume label.
CYGNUM_FS_MMFS_BLOCK_SIZE
This option defines the size of filesystem blocks. The value is
defined in KiB and must be a power of 2.
Default value: 256
CYGNUM_FS_MMFS_ROOTDIR_SIZE
This option defines the size of the root directory in blocks. Since
all files are contained in this directory, its size gives a hard limit
to the number of files that the filesystem may contain.
Default value: 1
CYGNUM_FS_MMFS_BAT_SIZE
This option defines the size of the Block Allocation Tables used to
store the addresses of file data blocks. This gives a hard upper limit on
the size of a file.
Default value: 2
CYGNUM_FS_MMFS_BAT_COUNT
This option defines the number of BATs allocated in the
filesystem. The default is to define 200 BATs.
These options control the memory footprint and other parameters for an
active filesystem.
CYGNUM_FS_MMFS_FILE_COUNT
This option defines the maximum number of open files supported by the
filesystem. This depends on the expected number of data streams, plus
any random access files, that may be open simultaneously.
Default value: 4
CYGNUM_FS_MMFS_DIRNODE_COUNT
This option defines the maximum number of cached directory entries. At
least one is required for each open file, plus a few for handling
other filesystem operations such as renaming or deleting.
Default value: CYGNUM_FS_MMFS_FILE_COUNT+4
CYGNUM_FS_MMFS_MULTI_BUFFER
This defines the level of per-file multi-buffering. During streaming
the filesystem will read ahead and write behind by this number of data
blocks.
Default value: 2
CYGNUM_FS_MMFS_DATA_CACHE_SIZE
This defines the amount of memory occupied by the data cache. The
default value is calculated from the multi-buffering level, and the
number of files.
This defines the amount of memory occupied by the metadata cache. The
default value is calculated from the number of files plus an overhead
to support the freelist and directory scanning.
This defines the size of a metadata cache block. These are used to
contain portions of the the directory, freelist and BATs.
Default value: 4
CYGNUM_FS_MMFS_DISKIO_PRIORITY
This defines the priority of the disk IO thread. This thread should
generally run at a high priority since it does very little but it is
vital to the performance of the filesystem.
Default value: 4
CYGNUM_FS_MMFS_FLUSH_INTERVAL
This defines the interval at which metadata cache blocks are flushed.
Each time this interval expires the oldest dirty block in the cache is
written to disk. This allows dirty data to be trickled out to disk
without severely impacting streaming transfers.
Default value: 10
CYGNUM_FS_MMFS_FLUSH_PERIOD
This defines the cache flush period in multiples of the cache flush
interval. Each time this period expires, the entire metadata cache
will be flushed to disk. The action of the flush interval will
generally cause this operation to do nothing.
