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Sun, 9 Nov 2025 14:50:16 GMT (envelope-from git) Date: Sun, 9 Nov 2025 14:50:16 GMT Message-Id: <202511091450.5A9EoG40004962@gitrepo.freebsd.org> To: src-committers@FreeBSD.org, dev-commits-src-all@FreeBSD.org, dev-commits-src-main@FreeBSD.org From: Mateusz Piotrowski <0mp@FreeBSD.org> Subject: git: 39acb7fd86ed - main - geom_zero.4: Document List-Id: Commit messages for the main branch of the src repository List-Archive: https://lists.freebsd.org/archives/dev-commits-src-main List-Help: List-Post: List-Subscribe: List-Unsubscribe: X-BeenThere: dev-commits-src-main@freebsd.org Sender: owner-dev-commits-src-main@FreeBSD.org MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 8bit X-Git-Committer: 0mp X-Git-Repository: src X-Git-Refname: refs/heads/main X-Git-Reftype: branch X-Git-Commit: 39acb7fd86eda721df402c2f1368b78cede161c3 Auto-Submitted: auto-generated The branch main has been updated by 0mp: URL: https://cgit.FreeBSD.org/src/commit/?id=39acb7fd86eda721df402c2f1368b78cede161c3 commit 39acb7fd86eda721df402c2f1368b78cede161c3 Author: Mateusz Piotrowski <0mp@FreeBSD.org> AuthorDate: 2025-11-09 14:46:40 +0000 Commit: Mateusz Piotrowski <0mp@FreeBSD.org> CommitDate: 2025-11-09 14:49:23 +0000 geom_zero.4: Document PR: 250593 Reviewed by: bcr, ziaee Thanks to: imp, markj MFC after: 1 week Fixes: 3843eba85d98 Add unmapped BIO support to GEOM ZERO Fixes: 24e1fdcd1a69 Allow to specify the byte which will be used for filling read buffer Fixes: 565bc101112c Add a very simple and small GEOM class - ZERO --- share/man/man4/Makefile | 2 + share/man/man4/geom_zero.4 | 174 +++++++++++++++++++++++++++++++++++++++++++++ share/man/man4/zero.4 | 3 +- 3 files changed, 178 insertions(+), 1 deletion(-) diff --git a/share/man/man4/Makefile b/share/man/man4/Makefile index fe1d285aec96..752ae9f165ca 100644 --- a/share/man/man4/Makefile +++ b/share/man/man4/Makefile @@ -189,6 +189,7 @@ MAN= aac.4 \ geom.4 \ geom_linux_lvm.4 \ geom_uzip.4 \ + geom_zero.4 \ gif.4 \ ${_gve.4} \ gpio.4 \ @@ -1123,6 +1124,7 @@ MAN+= \ veriexec.4 \ zyd.4 +MLINKS+=geom_zero.4 gzero.4 MLINKS+=mtw.4 if_mtw.4 MLINKS+=otus.4 if_otus.4 MLINKS+=rsu.4 if_rsu.4 diff --git a/share/man/man4/geom_zero.4 b/share/man/man4/geom_zero.4 new file mode 100644 index 000000000000..8da09b1473c9 --- /dev/null +++ b/share/man/man4/geom_zero.4 @@ -0,0 +1,174 @@ +.\" +.\" Copyright (c) 2019 Greg White . All rights reserved. +.\" Copyright (c) 2025 Mateusz Piotrowski <0mp@FreeBSD.org> +.\" +.\" SPDX-License-Identifier: BSD-2-Clause +.\" +.Dd November 9, 2025 +.Dt GEOM_ZERO 4 +.Os +.Sh NAME +.Nm gzero , +.Nm geom_zero +.Nd GEOM-based zero disk/block device +.Sh SYNOPSIS +.Cd "options GEOM_ZERO" +.Pp +In +.Xr loader.conf 5 +or +.Xr sysctl.conf 5 : +.Cd kern.geom.zero.byte +.Cd kern.geom.zero.clear +.Sh DESCRIPTION +.Nm +is a +.Xr GEOM 4 +device simulating a one-exabyte disk. +It throws away any data written to it, +and returns the value of +.Va kern.geom.zero.byte +for every byte read from it. +.Pp +.Nm +differs from +.Xr zero 4 , +which is a regular character device and has an infinite length, +while +.Pa /dev/gzero +is a +.Xr GEOM 4 +provider of large, but limited, size. +.Pp +Consult +.Xr geom 8 +for instructions on how to use the supported commands of the +.Xr GEOM 4 +.Nm ZERO +class. +.Pp +.Nm +is useful for benchmarking performance of GEOM and GEOM classes +where compression of the data does not affect the results +.Po blocks from +.Pa /dev/gzero +compress exceptionally well +.Pc . +Examples of such benchmarks include +comparing the speed of two disk encryption algorithms and +comparing a hardware versus software implementation +of a single encryption algorithm. +.Sh MIB VARIABLES +The following variables are available as both +.Xr sysctl 8 +variables and +.Xr loader 8 +tunables: +.Bl -tag -width "kern.geom.zero.clear" +.It Va kern.geom.zero.byte +This variable sets the fill byte of the +.Nm +device. +Default: +.Ql 0 . +.It Va kern.geom.zero.clear +This variable controls the clearing of the read data buffer. +If set to +.Ql 0 , +.Nm +will not copy any data into the read data buffers +and just return the read data buffers as they are without modifying them. +In particular, it will not not fill the read buffer with the value of +.Va kern.geom.zero.byte . +This is useful for read benchmarking to reduce the measurement noise +caused by extra memory initialization. +Default: +.Ql 1 . +.El +.Sh FILES +.Bl -tag -width /dev/gzero +.It Pa /dev/gzero +The +.Nm +device. +.El +.Sh EXAMPLES +Create the +.Pa /dev/gzero +device by loading the +.Nm geom_zero +kernel module: +.Bd -literal -offset indent +# geom zero load +.Ed +.Pp +Show information about the +.Nm +device: +.Bd -literal -offset indent +# geom zero list +Geom name: gzero +Providers: +1. Name: gzero + Mediasize: 1152921504606846976 (1.0E) + Sectorsize: 512 + Mode: r0w0egzero0 +.Ed +.Pp +Set the fill byte of the +.Nm +device to 70 +.Po decimal for letter +.Dq F +in +.Xr ascii 7 +.Pc : +.Bd -literal -offset indent +# sysctl kern.geom.zero.byte=70 +kern.geom.zero.byte: 0 -> 70 +# head -c 1 /dev/gzero +F +.Ed +.Pp +Benchmark read and write throughput of +.Xr geli 8 Ap s +default encryption algorithm with a 4-KiB sector size: +.Bd -literal -offset indent +# geom zero load +# geli onetime -s 4096 gzero +# sysctl kern.geom.zero.clear=0 +# dd if=/dev/gzero.eli of=/dev/zero bs=4k count=$((1024 * 256)) +262144+0 records in +262144+0 records out +1073741824 bytes transferred in 1.258195 secs (853398307 bytes/sec) +# dd if=/dev/zero of=/dev/gzero.eli bs=4k count=$((1024 * 256)) +262144+0 records in +262144+0 records out +1073741824 bytes transferred in 1.663118 secs (645619658 bytes/sec) +.Ed +.Sh SEE ALSO +.Xr GEOM 4 , +.Xr zero 4 , +.Xr geom 8 , +.Xr sysctl 8 , +.Xr bio 9 +.Sh HISTORY +A +.Nm +device first appeared in +.Fx 6 . +.Sh AUTHORS +.An -nosplit +The +.Nm +device was written by +.An Paweł Jakub Dawidek Aq Mt pjd@FreeBSD.org . +.Pp +The +.Nm +manual page was originally written by +.An Greg White Aq Mt gkwhite@gmail.com +and rewritten by +.An Mateusz Piotrowski Aq Mt 0mp@FreeBSD.org +before landing in +.Fx . diff --git a/share/man/man4/zero.4 b/share/man/man4/zero.4 index f1cd52d455d1..85651d53d342 100644 --- a/share/man/man4/zero.4 +++ b/share/man/man4/zero.4 @@ -29,7 +29,7 @@ .\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF .\" SUCH DAMAGE. .\" -.Dd April 7, 1996 +.Dd November 9, 2025 .Dt ZERO 4 .Os .Sh NAME @@ -48,6 +48,7 @@ supply of null bytes when read. .El .Sh SEE ALSO .Xr full 4 , +.Xr gzero 4 , .Xr null 4 .Sh HISTORY A