269 lines
4.9 KiB
Text
269 lines
4.9 KiB
Text
.TH FS 3
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.SH NAME
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fs \- file system devices
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.SH SYNOPSIS
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.nf
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.B bind -b #k /dev
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.sp 0.3v
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.B /dev/fs
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.B /dev/fs/ctl
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.B /dev/fs/...
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.B /dev/\fInew\fP
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.fi
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.SH DESCRIPTION
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The
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.I fs
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driver builds complex disk files out of simpler disk files.
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Inspired by the Plan 9 file server kernel's configuration strings,
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it provides device mirroring, partitioning, interleaving, and catenation
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for disk-based services like
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.IR venti (8).
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.PP
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The device is intended to be bound at
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.B /dev
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and initially contains a directory named
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.BR fs ,
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which in turn contains a
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.B ctl
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file and one file per configured device.
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.PP
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Most control messages introduce a new device, here named
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.IR new .
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The
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.I file
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arguments are interpreted in the name space of the writing process.
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.PP
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The device name
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.I new
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may be a single filename component (containing no slashes);
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in this case, the device is created under
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.BR #k/fs .
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If
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.I new
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instead has the format
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.IB dir / file,
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the device is made available at
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.BI #k/ dir / file.
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The directory
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.I dir
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goes away when the last device on it is removed with the
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.B del
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control message,
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but
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.B #k/fs
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will never be removed.
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.TF "del \fIold
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.PD
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.TP
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.BI cat " new files" \fR...
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The device
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.I new
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corresponds to the catenation of
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.IR files .
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.TP
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.BI inter " new files" \fR...
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The device
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.I new
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corresponds to the block interleaving of
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.IR files ;
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an 8192-byte block size is assumed.
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.TP
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.BI mirror " new files" \fR...
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The device
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.I new
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corresponds to a RAID-1-like mirroring of
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.IR files .
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Writes to
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.BI new
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are handled by sequentially writing the same data to the
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.I files
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from right to left (the reverse of
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the order in the control message).
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A failed write causes an eventual error return
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but does not prevent the rest of the writes
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to the other devices of the mirror set.
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Reads from
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.BI new
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are handled by sequentially reading from the
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.I files
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from left to right until one succeeds.
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The length of the mirror device is the minimum of the lengths of the
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.IR files .
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.TP
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.BI part " new file offset length"
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.TP
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.BI part " new offset end
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In the first form,
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the device
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.I new
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corresponds to the
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.I length
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units starting at
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.I offset
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in
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.IR file .
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If
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.IR offset + length
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reaches past the end of
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.IR file ,
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.I length
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is silently reduced to fit.
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Units are bytes.
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In the second form,
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a previous
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.B disk
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request must have defined the source
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.I file
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for further requests and the end of the device
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is determined by the
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.I end
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offset in the source file, and not by the device
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length. Units are as defined in the previous
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.B disk
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request. This form is accepted for compatibility with
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.IR fdisk
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(in
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.IR prep (8))
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and
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.IR sd (3)
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devices.
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.TP
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.BI del " old
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Removes the device named
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.IR old .
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The device will still be seen while in use.
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Further I/O attempts will fail with an error indication stating that
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the device is gone.
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When
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.I old
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is
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.IB dir /*\fR,
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all devices under
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.I dir
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are removed.
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.TP
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.BI disk " dir [ n file ]
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makes
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.I dir
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implicit in new device names (i.e., it makes
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.I new
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mean
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.IB dir / new
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by default).
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Optional argument
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.I n
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specifies the default unit (sector) size in bytes and the default source
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.I file
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for further partition devices.
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Default values are restored when the control file is closed.
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.TP
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.BI crypt " new file key"
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The device
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.I new
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corresponds to a AES-encrypted partition
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.I file
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encrypted with
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.I key (see
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.IR cryptsetup (8)).
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.TP
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.B clear
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Discard all
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.I fs
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device definitions.
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.PD
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.LP
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If the variable
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.B fsconfig
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is set in
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.IR plan9.ini (8),
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.I fs
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will read its configuration from the file
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.B $fsconfig
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on the first attach.
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This is useful when the machine boots from a local file server that uses
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.IR fs .
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.SH EXAMPLES
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Use a previously partitioned disk,
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.BR /dev/sdC0 ,
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making
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partition files available under
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.BR /dev/sdC0parts :
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.IP
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.EX
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{
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echo disk sdC0parts 512 /dev/sdC0/data
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disk/fdisk -p /dev/sdC0/data
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# now create plan 9 partitions
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echo disk sdC0parts 512 /dev/sdC0parts/plan9
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disk/prep -p /dev/sdC0parts/plan9
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} > /dev/fs/ctl
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.EE
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.LP
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Mirror the two disks
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.B /dev/sdC0/data
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and
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.B /dev/sdD0/data
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as
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.BR /dev/fs/m0 ;
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similarly, mirror
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.B /dev/sdC1/data
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and
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.B /dev/sdD1/data
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as
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.BR /dev/fs/m1 :
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.IP
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.EX
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echo mirror m0 /dev/sdC0/data /dev/sdD0/data >/dev/fs/ctl
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echo mirror m1 /dev/sdC1/data /dev/sdD1/data >/dev/fs/ctl
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.EE
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.LP
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Interleave the two mirrored disks to create
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.BR /dev/fs/data :
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.IP
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.EX
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echo inter data /dev/fs/m0 /dev/fs/m1 >/dev/fs/ctl
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.EE
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.LP
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Run
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.IR hjfs (4)
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on the interleaved device:
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.IP
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.EX
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hjfs -f /dev/fs/data
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.EE
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.LP
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Save the configuration:
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.IP
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.EX
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cp /dev/fs/ctl /dev/fd0disk
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.EE
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.LP
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To load the configuration automatically at boot time,
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add this to
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.IR plan9.ini :
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.IP
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.EX
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fsconfig=/dev/fd0disk
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.EE
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.SH "SEE ALSO"
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.I read
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in
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.IR cat (1),
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.IR dd (1),
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.IR sd (3),
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.IR fs (8),
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.IR plan9.ini (8),
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.IR prep (8),
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.IR venti (8)
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.SH SOURCE
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.B /sys/src/9/port/devfs.c
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.SH BUGS
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Mirrors are RAID-like but not RAID.
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There is no fancy recovery mechanism and
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no automatic initial copying from a master drive to its mirror drives.
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.PP
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Each
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.I write
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system call on
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.B ctl
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may transmit at most one command.
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