DBFS(4) DBFS(4)
NAME
dbfs, rawdbfs - simple database file system
SYNOPSIS
dbfs [ -abrce ] file mountpoint
rawdbfs [ -abrce ] file mountpoint
mountpoint/new
mountpoint/0
mountpoint/1
mountpoint/...
DESCRIPTION
Dbfs and rawdbfs both expose a simple, record-based filesys-
tem stored in file. The -a, -b, -c, and -r options have the
same meaning as the options accepted by bind(1). If the -e
option is given, then file will be created if it does not
already exist. The filesystem provided by both dbfs and
rawdbfs is substantially the same: when started, mountpoint
is populated with numbered files, one for each record found
in file. A read of one of these files yields the data in the
record; a write stores data in the record. A new record can
be created by opening the new file; writes to this file
write to the new record. The name of the new file can be
discovered by using fstat in sys-stat(2). Records can be
removed by removing the appropriate record file.
Dbfs and rawdbfs differ in the way that they store their
data. Dbfs stores its records in file in a simple text for-
mat: the end of a record is indicated by an empty line. The
file is completely rewritten every time a record is written.
Storing records containing blank lines will lead to confu-
sion when the database is re-read. Rawdbfs can store arbi-
trary data, but the format of the data storage is known only
to itself. It does not rewrite the whole file on every
record change, so can be more suitable for flash-based stor-
age, where it is important to minimise the number of writes.
Note that the record numbers always get their initial num-
bering from the order of the records in file. You cannot
assume that the filename given to a record will remain the
same between runs of dbfs.
SOURCE
/appl/cmd/dbfs.b
/appl/cmd/rawdbfs.b
SEE ALSO
memfs(4), ramfile(4), wm-calendar(1)
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DBFS(4) DBFS(4)
BUGS
Write offsets are ignored, so the maximum amount of data
that can be stored in a record is ATOMICIO bytes (i.e. 8K).
There is no way to compact a file maintained by dbfs.
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