1.\" Copyright (c) 1993 University of Utah. 2.\" Copyright (c) 1980, 1989, 1991, 1993 3.\" The Regents of the University of California. All rights reserved. 4.\" Copyright (c) 2000 5.\" Poul-Henning Kamp All rights reserved. 6.\" 7.\" This code is derived from software contributed to Berkeley by 8.\" the Systems Programming Group of the University of Utah Computer 9.\" Science Department. 10.\" 11.\" Redistribution and use in source and binary forms, with or without 12.\" modification, are permitted provided that the following conditions 13.\" are met: 14.\" 1. Redistributions of source code must retain the above copyright 15.\" notice, this list of conditions and the following disclaimer. 16.\" 2. Redistributions in binary form must reproduce the above copyright 17.\" notice, this list of conditions and the following disclaimer in the 18.\" documentation and/or other materials provided with the distribution. 19.\" 3. Neither the name of the University nor the names of its contributors 20.\" may be used to endorse or promote products derived from this software 21.\" without specific prior written permission. 22.\" 23.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND 24.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 25.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 26.\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE 27.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 28.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 29.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 30.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 31.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 32.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 33.\" SUCH DAMAGE. 34.\" 35.\" @(#)vnconfig.8 8.1 (Berkeley) 6/5/93 36.\" from: src/usr.sbin/vnconfig/vnconfig.8,v 1.19 2000/12/27 15:30:29 37.\" 38.\" $FreeBSD$ 39.\" 40.Dd August 27, 2021 41.Dt MDCONFIG 8 42.Os 43.Sh NAME 44.Nm mdconfig 45.Nd create and control memory disks 46.Sh SYNOPSIS 47.Nm 48.Fl a 49.Fl t Ar type 50.Op Fl n 51.Oo Fl o Oo Cm no Oc Ns Ar option Oc ... 52.Op Fl f Ar file 53.Op Fl s Ar size 54.Op Fl S Ar sectorsize 55.Op Fl u Ar unit 56.Op Fl x Ar sectors/track 57.Op Fl y Ar heads/cylinder 58.Op Fl L Ar label 59.Nm 60.Fl d 61.Fl u Ar unit 62.Op Fl o Oo Cm no Oc Ns Ar force 63.Nm 64.Fl r 65.Fl u Ar unit 66.Fl s Ar size 67.Op Fl o Oo Cm no Oc Ns Ar force 68.Nm 69.Fl l 70.Op Fl n 71.Op Fl v 72.Op Fl f Ar file 73.Op Fl u Ar unit 74.Nm 75.Ar file 76.Sh DESCRIPTION 77The 78.Nm 79utility creates and controls 80.Xr md 4 81devices. 82.Pp 83Options indicate an action to be performed: 84.Bl -tag -width indent 85.It Fl a 86Attach a memory disk. 87This will configure and attach a memory disk with the 88parameters specified and attach it to the system. 89If the 90.Fl u Ar unit 91option is not provided, the newly created device name will be printed on stdout. 92.It Fl d 93Detach a memory disk from the system and release all resources. 94.It Fl r 95Resize a memory disk. 96.It Fl t Ar type 97Select the type of the memory disk. 98.Bl -tag -width "malloc" 99.It Cm malloc 100Storage for this type of memory disk is allocated with 101.Xr malloc 9 . 102This limits the size to the malloc bucket limit in the kernel. 103If the 104.Fl o Cm reserve 105option is not set, creating and filling a large 106malloc-backed memory disk is a very easy way to 107panic the system. 108.It Cm vnode 109A file specified with 110.Fl f Ar file 111becomes the backing store for this memory disk. 112.It Cm swap 113Storage for this type of memory disk is allocated from buffer 114memory. 115Pages get pushed out to swap when the system is under memory 116pressure, otherwise they stay in the operating memory. 117Using 118.Cm swap 119backing is generally preferred instead of using 120.Cm malloc 121backing. 122.It Cm null 123Bitsink; all writes do nothing, all reads return zeroes. 124.El 125.It Fl f Ar file 126Filename to use for the vnode type memory disk. 127The 128.Fl a 129and 130.Fl t Cm vnode 131options are implied if not specified. 132.It Fl l 133List configured devices. 134If given with 135.Fl u , 136display details about that particular device. 137If given with 138.Fl f Ar file , 139display 140.Xr md 4 141device names of which 142.Ar file 143is used as the backing store. 144If both of 145.Fl u 146and 147.Fl f 148options are specified, 149display devices which match the two conditions. 150If the 151.Fl v 152option is specified, show all details. 153.It Fl n 154When printing 155.Xr md 4 156device names, print only the unit number without the 157.Xr md 4 158prefix. 159.It Fl s Ar size 160Size of the memory disk. 161.Ar Size 162is the number of 512 byte sectors unless suffixed with a 163.Cm b , k , m , g , t , 164or 165.Cm p 166which 167denotes byte, kilobyte, megabyte, gigabyte, terabyte and petabyte respectively. 168When used without the 169.Fl r 170option, the 171.Fl a 172and 173.Fl t Cm swap 174options are implied if not specified. 175.It Fl S Ar sectorsize 176Sectorsize to use for the memory disk, in bytes. 177.It Fl x Ar sectors/track 178See the description of the 179.Fl y 180option below. 181.It Fl y Ar heads/cylinder 182For 183.Cm malloc 184or 185.Cm vnode 186backed devices, the 187.Fl x 188and 189.Fl y 190options can be used to specify a synthetic geometry. 191This is useful for constructing bootable images for later download to 192other devices. 193.It Fl L Ar label 194Associate a label (arbitrary string) with the new memory disk. 195The label can then be inspected with 196.Bd -literal -offset indent 197.Nm Fl l v 198.Ed 199.It Fl o Oo Cm no Oc Ns Ar option 200Set or reset options. 201.Bl -tag -width indent 202.It Oo Cm no Oc Ns Cm async 203For 204.Cm vnode 205backed devices: avoid 206.Dv IO_SYNC 207for increased performance but 208at the risk of deadlocking the entire kernel. 209.It Oo Cm no Oc Ns Cm cache 210For 211.Cm vnode 212backed devices: enable/disable caching of data in system caches. 213The default is to not cache. 214.Pp 215Accesses via the device are converted to accesses via the vnode. 216The caching policy for the vnode is used initially. 217This is normally to cache. 218This caching policy is retained if the 219.Cm cache 220option is used. 221Otherwise, caching is limited 222by releasing data from caches soon after each access. 223The release has the same semantics as the 224.Dv POSIX_FADV_DONTNEED 225feature of 226.Xr posix_fadvise 2 . 227The result is that with normal (non-zfs) caching, 228buffers are released from the buffer cache soon after they are constructed, 229but their data is kept in the page cache at lower priority. 230.Pp 231The 232.Cm cache 233option tends to waste memory by giving unwanted double caching, 234but it saves time if there is memory to spare. 235.It Oo Cm no Oc Ns Cm reserve 236Allocate and reserve all needed storage from the start, rather than as needed. 237.It Oo Cm no Oc Ns Cm cluster 238Enable clustering on this disk. 239.It Oo Cm no Oc Ns Cm compress 240Enable/disable compression features to reduce memory usage. 241.It Oo Cm no Oc Ns Cm force 242Disable/enable extra sanity checks to prevent the user from doing something 243that might adversely affect the system. 244This can be used with the 245.Fl d 246flag to forcibly destroy an 247.Xr md 4 248disk that is still in use. 249.It Oo Cm no Oc Ns Cm mustdealloc 250For 251.Cm vnode 252backed devices: detect whether hole-punching is supported by the underlying file 253system. 254If the file system supports hole-punching, then to handle a 255.Dv BIO_DELETE 256request, some or all of the request's operation range may be turned into a hole 257in the file used for backing store. 258Any parts which are not turned into holes are zero-filled in 259the file. 260If the file system does not support 261hole-punching, 262.Dv BIO_DELETE 263requests to the device are not handled and will fail with 264.Er EOPNOTSUPP . 265.Pp 266When 267.Cm mustdealloc 268is not specified or 269.Oo Cm no Oc Ns Cm mustdealloc 270is specified, for a 271.Dv BIO_DELETE 272request, if the file system supports hole-punching, some or all of the request's 273operation range may be turned into a hole in the file used for backing store. 274Any parts which are not turned into holes are zero-filled in the file. 275If the file system of the vnode type memory disk does not support hole-punching, 276the request's operation range is zero-filled in the file. 277.It Oo Cm no Oc Ns Cm readonly 278Enable/disable readonly mode. 279.It Oo Cm no Oc Ns Cm verify 280For 281.Cm vnode 282backed devices: enable/disable requesting verification of the 283file used for backing store. 284The type of verification depends on which security features are available. 285One example of verification is testing file integrity with 286checksums or cryptographic signatures. 287.El 288.It Fl u Ar unit 289Request a specific unit number or device name for the 290.Xr md 4 291device instead of automatic allocation. 292If a device name is specified, it must start with 293.Dq md 294followed by the unit number. 295.El 296.Pp 297The last form, 298.Nm 299.Ar file , 300is provided for convenience as an abbreviation of 301.Nm 302.Fl a 303.Fl t Cm vnode 304.Fl f Ar file . 305.Sh EXAMPLES 306Create a disk with 307.Pa /tmp/boot.flp 308as backing storage. 309The name of the allocated unit will be printed on stdout, such as 310.Dq Li md0 : 311.Bd -literal -offset indent 312mdconfig /tmp/boot.flp 313.Ed 314.Pp 315Create a 1 gigabyte swap backed memory disk named 316.Dq Li md3 : 317.Bd -literal -offset indent 318mdconfig -s 1g -u md3 319.Ed 320.Pp 321Detach and free all resources used by 322.Pa /dev/md3 : 323.Bd -literal -offset indent 324mdconfig -du md3 325.Ed 326.Pp 327Show detailed information on current memory disks: 328.Bd -literal -offset indent 329mdconfig -lv 330.Ed 331.Pp 332Resize the 333.Dq Li md3 334memory disk to 2 gigabytes: 335.Bd -literal -offset indent 336mdconfig -rs 2g -u md3 337.Ed 338.Pp 339Create a 1 gigabyte swap backed disk, initialize an 340.Xr ffs 7 341file system on it, and mount it on 342.Pa /tmp : 343.Bd -literal -offset indent 344mdconfig -s 1g -u md10 345newfs -U /dev/md10 346mount /dev/md10 /tmp 347chmod 1777 /tmp 348.Ed 349.Pp 350Create a memory disk out of an ISO 9660 CD image file, 351using the first available 352.Xr md 4 353device, and then mount it: 354.Bd -literal -offset indent 355mount -t cd9660 /dev/`mdconfig -f cdimage.iso` /mnt 356.Ed 357.Pp 358Create a file-backed device from a hard disk image that begins 359with 512K of raw header information. 360.Xr gnop 8 361is used to skip over the header information, positioning 362.Pa md1.nop 363to the start of the filesystem in the image. 364.Bd -literal -offset indent 365mdconfig -u md1 -f diskimage.img 366gnop create -o 512K md1 367mount /dev/md1.nop /mnt 368.Ed 369.Sh SEE ALSO 370.Xr fpathconf 2 , 371.Xr fspacectl 2 , 372.Xr open 2 , 373.Xr md 4 , 374.Xr ffs 7 , 375.Xr gpart 8 , 376.Xr mdmfs 8 , 377.Xr malloc 9 , 378.Xr vn_deallocate 9 379.Sh HISTORY 380The 381.Nm 382utility first appeared in 383.Fx 5.0 384as a cleaner replacement for the vn kernel module 385and the vnconfig utility combo. 386.Sh AUTHORS 387The 388.Nm 389utility was written by 390.An Poul-Henning Kamp Aq Mt phk@FreeBSD.org . 391