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.\" from: src/usr.sbin/vnconfig/vnconfig.8,v 1.19 2000/12/27 15:30:29 35.\" 36.Dd June 1, 2024 37.Dt MDCONFIG 8 38.Os 39.Sh NAME 40.Nm mdconfig 41.Nd create and control memory disks 42.Sh SYNOPSIS 43.Nm 44.Fl a 45.Fl t Ar type 46.Op Fl n 47.Oo Fl o Oo Cm no Oc Ns Ar option Oc ... 48.Op Fl f Ar file 49.Op Fl s Ar size 50.Op Fl S Ar sectorsize 51.Op Fl u Ar unit 52.Op Fl x Ar sectors/track 53.Op Fl y Ar heads/cylinder 54.Op Fl L Ar label 55.Nm 56.Fl d 57.Fl u Ar unit 58.Op Fl o Oo Cm no Oc Ns Ar force 59.Nm 60.Fl r 61.Fl u Ar unit 62.Fl s Ar size 63.Op Fl o Oo Cm no Oc Ns Ar force 64.Nm 65.Fl l 66.Op Fl n 67.Op Fl v 68.Op Fl f Ar file 69.Op Fl u Ar unit 70.Nm 71.Ar file 72.Sh DESCRIPTION 73The 74.Nm 75utility creates and controls 76.Xr md 4 77devices. 78.Pp 79Options indicate an action to be performed: 80.Bl -tag -width indent 81.It Fl a 82Attach a memory disk. 83This will configure and attach a memory disk with the 84parameters specified and attach it to the system. 85If the 86.Fl u Ar unit 87option is not provided, the newly created device name will be printed on stdout. 88.It Fl d 89Detach a memory disk from the system and release all resources. 90.It Fl r 91Resize a memory disk. 92.It Fl t Ar type 93Select the type of the memory disk. 94.Bl -tag -width "malloc" 95.It Cm malloc 96Storage for this type of memory disk is allocated with 97.Xr malloc 9 . 98This limits the size to the malloc bucket limit in the kernel. 99If the 100.Fl o Cm reserve 101option is not set, creating and filling a large 102malloc-backed memory disk is a very easy way to 103panic the system. 104.It Cm vnode 105A file specified with 106.Fl f Ar file 107becomes the backing store for this memory disk. 108.It Cm swap 109Storage for this type of memory disk is allocated from buffer 110memory. 111Pages get pushed out to swap when the system is under memory 112pressure, otherwise they stay in the operating memory. 113Using 114.Cm swap 115backing is generally preferred instead of using 116.Cm malloc 117backing. 118.It Cm null 119Bitsink; all writes do nothing, all reads return zeroes. 120.El 121.It Fl f Ar file 122Filename to use for the vnode type memory disk. 123The 124.Fl a 125and 126.Fl t Cm vnode 127options are implied if not specified. 128.It Fl l 129List configured devices. 130If given with 131.Fl u , 132display details about that particular device. 133If given with 134.Fl f Ar file , 135display 136.Xr md 4 137device names of which 138.Ar file 139is used as the backing store. 140If both of 141.Fl u 142and 143.Fl f 144options are specified, 145display devices which match the two conditions. 146If the 147.Fl v 148option is specified, show all details. 149.It Fl n 150When printing 151.Xr md 4 152device names, print only the unit number without the 153.Xr md 4 154prefix. 155.It Fl s Ar size 156Size of the memory disk. 157.Ar Size 158is the number of 512 byte sectors unless suffixed with a 159.Cm b , k , m , g , t , 160or 161.Cm p 162which 163denotes byte, kilobyte, megabyte, gigabyte, terabyte and petabyte respectively. 164When used without the 165.Fl r 166option, the 167.Fl a 168and 169.Fl t Cm swap 170options are implied if not specified. 171.It Fl S Ar sectorsize 172Sectorsize to use for the memory disk, in bytes. 173.It Fl x Ar sectors/track 174See the description of the 175.Fl y 176option below. 177.It Fl y Ar heads/cylinder 178For 179.Cm malloc 180or 181.Cm vnode 182backed devices, the 183.Fl x 184and 185.Fl y 186options can be used to specify a synthetic geometry. 187This is useful for constructing bootable images for later download to 188other devices. 189.It Fl L Ar label 190Associate a label (arbitrary string) with the new memory disk. 191The label can then be inspected with 192.Bd -literal -offset indent 193.Nm Fl l v 194.Ed 195.It Fl o Oo Cm no Oc Ns Ar option 196Set or reset options. 197.Bl -tag -width indent 198.It Oo Cm no Oc Ns Cm async 199For 200.Cm vnode 201backed devices: avoid 202.Dv IO_SYNC 203for increased performance but 204at the risk of deadlocking the entire kernel. 205.It Oo Cm no Oc Ns Cm cache 206For 207.Cm vnode 208backed devices: enable/disable caching of data in system caches. 209The default is to not cache. 210.Pp 211Accesses via the device are converted to accesses via the vnode. 212The caching policy for the vnode is used initially. 213This is normally to cache. 214This caching policy is retained if the 215.Cm cache 216option is used. 217Otherwise, caching is limited 218by releasing data from caches soon after each access. 219The release has the same semantics as the 220.Dv POSIX_FADV_DONTNEED 221feature of 222.Xr posix_fadvise 2 . 223The result is that with normal (non-zfs) caching, 224buffers are released from the buffer cache soon after they are constructed, 225but their data is kept in the page cache at lower priority. 226.Pp 227The 228.Cm cache 229option tends to waste memory by giving unwanted double caching, 230but it saves time if there is memory to spare. 231.It Oo Cm no Oc Ns Cm reserve 232Allocate and reserve all needed storage from the start, rather than as needed. 233.It Oo Cm no Oc Ns Cm compress 234Enable/disable compression features to reduce memory usage. 235.It Oo Cm no Oc Ns Cm force 236Disable/enable extra sanity checks to prevent the user from doing something 237that might adversely affect the system. 238This can be used with the 239.Fl d 240flag to forcibly destroy an 241.Xr md 4 242disk that is still in use. 243.It Oo Cm no Oc Ns Cm mustdealloc 244For 245.Cm vnode 246backed devices: detect whether hole-punching is supported by the underlying file 247system. 248If the file system supports hole-punching, then to handle a 249.Dv BIO_DELETE 250request, some or all of the request's operation range may be turned into a hole 251in the file used for backing store. 252Any parts which are not turned into holes are zero-filled in 253the file. 254If the file system does not support 255hole-punching, 256.Dv BIO_DELETE 257requests to the device are not handled and will fail with 258.Er EOPNOTSUPP . 259.Pp 260When 261.Cm mustdealloc 262is not specified or 263.Oo Cm no Oc Ns Cm mustdealloc 264is specified, for a 265.Dv BIO_DELETE 266request, if the file system supports hole-punching, some or all of the request's 267operation range may be turned into a hole in the file used for backing store. 268Any parts which are not turned into holes are zero-filled in the file. 269If the file system of the vnode type memory disk does not support hole-punching, 270the request's operation range is zero-filled in the file. 271.It Oo Cm no Oc Ns Cm readonly 272Enable/disable readonly mode. 273.It Oo Cm no Oc Ns Cm verify 274For 275.Cm vnode 276backed devices: enable/disable requesting verification of the 277file used for backing store. 278The type of verification depends on which security features are available. 279One example of verification is testing file integrity with 280checksums or cryptographic signatures. 281.El 282.It Fl u Ar unit 283Request a specific unit number or device name for the 284.Xr md 4 285device instead of automatic allocation. 286If a device name is specified, it must start with 287.Dq md 288followed by the unit number. 289.El 290.Pp 291The last form, 292.Nm 293.Ar file , 294is provided for convenience as an abbreviation of 295.Nm 296.Fl a 297.Fl t Cm vnode 298.Fl f Ar file . 299.Sh EXAMPLES 300Create a disk with 301.Pa /tmp/boot.flp 302as backing storage. 303The name of the allocated unit will be printed on stdout, such as 304.Dq Li md0 : 305.Bd -literal -offset indent 306mdconfig /tmp/boot.flp 307.Ed 308.Pp 309Create a 1 gigabyte swap backed memory disk named 310.Dq Li md3 : 311.Bd -literal -offset indent 312mdconfig -s 1g -u md3 313.Ed 314.Pp 315Detach and free all resources used by 316.Pa /dev/md3 : 317.Bd -literal -offset indent 318mdconfig -du md3 319.Ed 320.Pp 321Show detailed information on current memory disks: 322.Bd -literal -offset indent 323mdconfig -lv 324.Ed 325.Pp 326Resize the 327.Dq Li md3 328memory disk to 2 gigabytes: 329.Bd -literal -offset indent 330mdconfig -rs 2g -u md3 331.Ed 332.Pp 333Create a 1 gigabyte swap backed disk, initialize an 334.Xr ffs 4 335file system on it, and mount it on 336.Pa /tmp : 337.Bd -literal -offset indent 338mdconfig -s 1g -u md10 339newfs -U /dev/md10 340mount /dev/md10 /tmp 341chmod 1777 /tmp 342.Ed 343.Pp 344Create a memory disk out of an ISO 9660 CD image file, 345using the first available 346.Xr md 4 347device, and then mount it: 348.Bd -literal -offset indent 349mount -t cd9660 /dev/`mdconfig -f cdimage.iso` /mnt 350.Ed 351.Pp 352Create a file-backed device from a hard disk image that begins 353with 512K of raw header information. 354.Xr gnop 8 355is used to skip over the header information, positioning 356.Pa md1.nop 357to the start of the filesystem in the image. 358.Bd -literal -offset indent 359mdconfig -u md1 -f diskimage.img 360gnop create -o 512K md1 361mount /dev/md1.nop /mnt 362.Ed 363.Sh SEE ALSO 364.Xr fpathconf 2 , 365.Xr fspacectl 2 , 366.Xr open 2 , 367.Xr ffs 4 , 368.Xr md 4 , 369.Xr gpart 8 , 370.Xr mdmfs 8 , 371.Xr malloc 9 , 372.Xr vn_deallocate 9 373.Sh HISTORY 374The 375.Nm 376utility first appeared in 377.Fx 5.0 378as a cleaner replacement for the vn kernel module 379and the vnconfig utility combo. 380.Sh AUTHORS 381The 382.Nm 383utility was written by 384.An Poul-Henning Kamp Aq Mt phk@FreeBSD.org . 385