ref: 6b989beb2f870c46363c1feba1a25c59add41d5a
dir: /sys/man/3/fs/
.TH FS 3 .SH NAME fs \- file system devices .SH SYNOPSIS .nf .B bind -b #k /dev .sp 0.3v .B /dev/fs .B /dev/fs/ctl .B /dev/fs/... .B /dev/\fInew\fP .fi .SH DESCRIPTION The .I fs driver builds complex disk files out of simpler disk files. Inspired by the Plan 9 file server kernel's configuration strings, it provides device mirroring, partitioning, interleaving, and catenation for disk-based services like .IR venti (8). .PP The device is intended to be bound at .B /dev and initially contains a directory named .BR fs , which in turn contains a .B ctl file and one file per configured device. .PP Most control messages introduce a new device, here named .IR new . The .I file arguments are interpreted in the name space of the writing process. .PP The device name .I new may be a single filename component (containing no slashes); in this case, the device is created under .BR #k/fs . If .I new instead has the format .IB dir / file, the device is made available at .BI #k/ dir / file. The directory .I dir goes away when the last device on it is removed with the .B del control message, but .B #k/fs will never be removed. .TF "del \fIold .PD .TP .BI cat " new files" \fR... The device .I new corresponds to the catenation of .IR files . .TP .BI inter " new files" \fR... The device .I new corresponds to the block interleaving of .IR files ; an 8192-byte block size is assumed. .TP .BI mirror " new files" \fR... The device .I new corresponds to a RAID-1-like mirroring of .IR files . Writes to .BI new are handled by sequentially writing the same data to the .I files from right to left (the reverse of the order in the control message). A failed write causes an eventual error return but does not prevent the rest of the writes to the other devices of the mirror set. Reads from .BI new are handled by sequentially reading from the .I files from left to right until one succeeds. The length of the mirror device is the minimum of the lengths of the .IR files . .TP .BI part " new file offset length" .TP .BI part " new offset end In the first form, the device .I new corresponds to the .I length units starting at .I offset in .IR file . If .IR offset + length reaches past the end of .IR file , .I length is silently reduced to fit. Units are bytes. In the second form, a previous .B disk request must have defined the source .I file for further requests and the end of the device is determined by the .I end offset in the source file, and not by the device length. Units are as defined in the previous .B disk request. This form is accepted for compatibility with .IR fdisk (in .IR prep (8)) and .IR sd (3) devices. .TP .BI del " old Removes the device named .IR old . The device will still be seen while in use. Further I/O attempts will fail with an error indication stating that the device is gone. When .I old is .IB dir /*\fR, all devices under .I dir are removed. .TP .BI disk " dir [ n file ] makes .I dir implicit in new device names (i.e., it makes .I new mean .IB dir / new by default). Optional argument .I n specifies the default unit (sector) size in bytes and the default source .I file for further partition devices. Default values are restored when the control file is closed. .TP .BI crypt " new file key" The device .I new corresponds to a AES-encrypted partition .I file encrypted with .I key (see .IR cryptsetup (8)). .TP .B clear Discard all .I fs device definitions. .PD .LP If the variable .B fsconfig is set in .IR plan9.ini (8), .I fs will read its configuration from the file .B $fsconfig on the first attach. This is useful when the machine boots from a local file server that uses .IR fs . .SH EXAMPLES Use a previously partitioned disk, .BR /dev/sdC0 , making partition files available under .BR /dev/sdC0parts : .IP .EX { echo disk sdC0parts 512 /dev/sdC0/data disk/fdisk -p /dev/sdC0/data # now create plan 9 partitions echo disk sdC0parts 512 /dev/sdC0parts/plan9 disk/prep -p /dev/sdC0parts/plan9 } > /dev/fs/ctl .EE .LP Mirror the two disks .B /dev/sdC0/data and .B /dev/sdD0/data as .BR /dev/fs/m0 ; similarly, mirror .B /dev/sdC1/data and .B /dev/sdD1/data as .BR /dev/fs/m1 : .IP .EX echo mirror m0 /dev/sdC0/data /dev/sdD0/data >/dev/fs/ctl echo mirror m1 /dev/sdC1/data /dev/sdD1/data >/dev/fs/ctl .EE .LP Interleave the two mirrored disks to create .BR /dev/fs/data : .IP .EX echo inter data /dev/fs/m0 /dev/fs/m1 >/dev/fs/ctl .EE .LP Run .IR hjfs (4) on the interleaved device: .IP .EX hjfs -f /dev/fs/data .EE .LP Save the configuration: .IP .EX cp /dev/fs/ctl /dev/fd0disk .EE .LP To load the configuration automatically at boot time, add this to .IR plan9.ini : .IP .EX fsconfig=/dev/fd0disk .EE .SH "SEE ALSO" .I read in .IR cat (1), .IR dd (1), .IR sd (3), .IR fs (8), .IR plan9.ini (8), .IR prep (8), .IR venti (8) .SH SOURCE .B /sys/src/9/port/devfs.c .SH BUGS Mirrors are RAID-like but not RAID. There is no fancy recovery mechanism and no automatic initial copying from a master drive to its mirror drives. .PP Each .I write system call on .B ctl may transmit at most one command.