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diff --git a/documentation/content/en/articles/geom-class/_index.po b/documentation/content/en/articles/geom-class/_index.po new file mode 100644 index 0000000000..ef0c661432 --- /dev/null +++ b/documentation/content/en/articles/geom-class/_index.po @@ -0,0 +1,1059 @@ +# SOME DESCRIPTIVE TITLE +# Copyright (C) YEAR The FreeBSD Project +# This file is distributed under the same license as the FreeBSD Documentation package. +# FIRST AUTHOR <EMAIL@ADDRESS>, YEAR. +# +#, fuzzy +msgid "" +msgstr "" +"Project-Id-Version: FreeBSD Documentation VERSION\n" +"POT-Creation-Date: 2022-02-01 09:21-0300\n" +"PO-Revision-Date: YEAR-MO-DA HO:MI+ZONE\n" +"Last-Translator: FULL NAME <EMAIL@ADDRESS>\n" +"Language-Team: LANGUAGE <LL@li.org>\n" +"Language: \n" +"MIME-Version: 1.0\n" +"Content-Type: text/plain; charset=UTF-8\n" +"Content-Transfer-Encoding: 8bit\n" + +#. type: YAML Front Matter: description +#: documentation/content/en/articles/geom-class/_index.adoc:1 +#, no-wrap +msgid "A guide to GEOM internals, and writing your own GEOM class" +msgstr "" + +#. type: Title = +#: documentation/content/en/articles/geom-class/_index.adoc:1 +#: documentation/content/en/articles/geom-class/_index.adoc:11 +#, no-wrap +msgid "Writing a GEOM Class" +msgstr "" + +#. type: Plain text +#: documentation/content/en/articles/geom-class/_index.adoc:44 +msgid "Abstract" +msgstr "" + +#. type: Plain text +#: documentation/content/en/articles/geom-class/_index.adoc:47 +msgid "" +"This text documents some starting points in developing GEOM classes, and " +"kernel modules in general. It is assumed that the reader is familiar with C " +"userland programming." +msgstr "" + +#. type: Plain text +#: documentation/content/en/articles/geom-class/_index.adoc:49 +msgid "'''" +msgstr "" + +#. type: Title == +#: documentation/content/en/articles/geom-class/_index.adoc:53 +#, no-wrap +msgid "Introduction" +msgstr "" + +#. type: Title === +#: documentation/content/en/articles/geom-class/_index.adoc:56 +#, no-wrap +msgid "Documentation" +msgstr "" + +#. type: Plain text +#: documentation/content/en/articles/geom-class/_index.adoc:60 +msgid "" +"Documentation on kernel programming is scarce - it is one of few areas where " +"there is nearly nothing in the way of friendly tutorials, and the phrase " +"\"use the source!\" really holds true. However, there are some bits and " +"pieces (some of them seriously outdated) floating around that should be " +"studied before beginning to code:" +msgstr "" + +#. type: Plain text +#: documentation/content/en/articles/geom-class/_index.adoc:62 +msgid "" +"The extref:{developers-handbook}[FreeBSD Developer's Handbook] - part of the " +"documentation project, it does not contain anything specific to kernel " +"programming, but rather some general useful information." +msgstr "" + +#. type: Plain text +#: documentation/content/en/articles/geom-class/_index.adoc:63 +msgid "" +"The extref:{arch-handbook}[FreeBSD Architecture Handbook] - also from the " +"documentation project, contains descriptions of several low-level facilities " +"and procedures. The most important chapter is 13, extref:{arch-handbook}" +"[Writing FreeBSD device drivers, driverbasics]." +msgstr "" + +#. type: Plain text +#: documentation/content/en/articles/geom-class/_index.adoc:64 +msgid "" +"The Blueprints section of http://www.freebsddiary.org[FreeBSD Diary] web " +"site - contains several interesting articles on kernel facilities." +msgstr "" + +#. type: Plain text +#: documentation/content/en/articles/geom-class/_index.adoc:65 +msgid "" +"The man pages in section 9 - for important documentation on kernel functions." +msgstr "" + +#. type: Plain text +#: documentation/content/en/articles/geom-class/_index.adoc:66 +msgid "" +"The man:geom[4] man page and http://phk.freebsd.dk/pubs/[PHK's GEOM slides] " +"- for general introduction of the GEOM subsystem." +msgstr "" + +#. type: Plain text +#: documentation/content/en/articles/geom-class/_index.adoc:67 +msgid "" +"Man pages man:g_bio[9], man:g_event[9], man:g_data[9], man:g_geom[9], man:" +"g_provider[9], man:g_consumer[9], man:g_access[9] & others linked from " +"those, for documentation on specific functionalities." +msgstr "" + +#. type: Plain text +#: documentation/content/en/articles/geom-class/_index.adoc:68 +msgid "" +"The man:style[9] man page - for documentation on the coding-style " +"conventions which must be followed for any code which is to be committed to " +"the FreeBSD tree." +msgstr "" + +#. type: Title == +#: documentation/content/en/articles/geom-class/_index.adoc:70 +#, no-wrap +msgid "Preliminaries" +msgstr "" + +#. type: Plain text +#: documentation/content/en/articles/geom-class/_index.adoc:77 +msgid "" +"The best way to do kernel development is to have (at least) two separate " +"computers. One of these would contain the development environment and " +"sources, and the other would be used to test the newly written code by " +"network-booting and network-mounting filesystems from the first one. This " +"way if the new code contains bugs and crashes the machine, it will not mess " +"up the sources (and other \"live\" data). The second system does not even " +"require a proper display. Instead, it could be connected with a serial " +"cable or KVM to the first one." +msgstr "" + +#. type: Plain text +#: documentation/content/en/articles/geom-class/_index.adoc:80 +msgid "" +"But, since not everybody has two or more computers handy, there are a few " +"things that can be done to prepare an otherwise \"live\" system for " +"developing kernel code. This setup is also applicable for developing in a " +"http://www.vmware.com/[VMWare] or http://www.qemu.org/[QEmu] virtual machine " +"(the next best thing after a dedicated development machine)." +msgstr "" + +#. type: Title === +#: documentation/content/en/articles/geom-class/_index.adoc:82 +#, no-wrap +msgid "Modifying a System for Development" +msgstr "" + +#. type: Plain text +#: documentation/content/en/articles/geom-class/_index.adoc:85 +msgid "" +"For any kernel programming a kernel with `INVARIANTS` enabled is a must-" +"have. So enter these in your kernel configuration file:" +msgstr "" + +#. type: delimited block . 4 +#: documentation/content/en/articles/geom-class/_index.adoc:90 +#, no-wrap +msgid "" +"options INVARIANT_SUPPORT\n" +"options INVARIANTS\n" +msgstr "" + +#. type: Plain text +#: documentation/content/en/articles/geom-class/_index.adoc:93 +msgid "" +"For more debugging you should also include WITNESS support, which will alert " +"you of mistakes in locking:" +msgstr "" + +#. type: delimited block . 4 +#: documentation/content/en/articles/geom-class/_index.adoc:98 +#, no-wrap +msgid "" +"options WITNESS_SUPPORT\n" +"options WITNESS\n" +msgstr "" + +#. type: Plain text +#: documentation/content/en/articles/geom-class/_index.adoc:101 +msgid "For debugging crash dumps, a kernel with debug symbols is needed:" +msgstr "" + +#. type: delimited block . 4 +#: documentation/content/en/articles/geom-class/_index.adoc:105 +#, no-wrap +msgid " makeoptions DEBUG=-g\n" +msgstr "" + +#. type: Plain text +#: documentation/content/en/articles/geom-class/_index.adoc:110 +msgid "" +"With the usual way of installing the kernel (`make installkernel`) the debug " +"kernel will not be automatically installed. It is called [.filename]#kernel." +"debug# and located in [.filename]#/usr/obj/usr/src/sys/KERNELNAME/#. For " +"convenience it should be copied to [.filename]#/boot/kernel/#." +msgstr "" + +#. type: Plain text +#: documentation/content/en/articles/geom-class/_index.adoc:113 +msgid "" +"Another convenience is enabling the kernel debugger so you can examine a " +"kernel panic when it happens. For this, enter the following lines in your " +"kernel configuration file:" +msgstr "" + +#. type: delimited block . 4 +#: documentation/content/en/articles/geom-class/_index.adoc:119 +#, no-wrap +msgid "" +"options KDB\n" +"options DDB\n" +"options KDB_TRACE\n" +msgstr "" + +#. type: Plain text +#: documentation/content/en/articles/geom-class/_index.adoc:122 +msgid "" +"For this to work you might need to set a sysctl (if it is not on by default):" +msgstr "" + +#. type: delimited block . 4 +#: documentation/content/en/articles/geom-class/_index.adoc:126 +#, no-wrap +msgid " debug.debugger_on_panic=1\n" +msgstr "" + +#. type: Plain text +#: documentation/content/en/articles/geom-class/_index.adoc:134 +msgid "" +"Kernel panics will happen, so care should be taken with the filesystem " +"cache. In particular, having softupdates might mean the latest file version " +"could be lost if a panic occurs before it is committed to storage. " +"Disabling softupdates yields a great performance hit, and still does not " +"guarantee data consistency. Mounting filesystem with the \"sync\" option is " +"needed for that. For a compromise, the softupdates cache delays can be " +"shortened. There are three sysctl's that are useful for this (best to be " +"set in [.filename]#/etc/sysctl.conf#):" +msgstr "" + +#. type: delimited block . 4 +#: documentation/content/en/articles/geom-class/_index.adoc:140 +#, no-wrap +msgid "" +"kern.filedelay=5\n" +"kern.dirdelay=4\n" +"kern.metadelay=3\n" +msgstr "" + +#. type: Plain text +#: documentation/content/en/articles/geom-class/_index.adoc:143 +msgid "The numbers represent seconds." +msgstr "" + +#. type: Plain text +#: documentation/content/en/articles/geom-class/_index.adoc:151 +msgid "" +"For debugging kernel panics, kernel core dumps are required. Since a kernel " +"panic might make filesystems unusable, this crash dump is first written to a " +"raw partition. Usually, this is the swap partition. This partition must be " +"at least as large as the physical RAM in the machine. On the next boot, the " +"dump is copied to a regular file. This happens after filesystems are " +"checked and mounted, and before swap is enabled. This is controlled with " +"two [.filename]#/etc/rc.conf# variables:" +msgstr "" + +#. type: delimited block . 4 +#: documentation/content/en/articles/geom-class/_index.adoc:156 +#, no-wrap +msgid "" +"dumpdev=\"/dev/ad0s4b\"\n" +"dumpdir=\"/usr/core\n" +msgstr "" + +#. type: Plain text +#: documentation/content/en/articles/geom-class/_index.adoc:159 +msgid "" +"The `dumpdev` variable specifies the swap partition and `dumpdir` tells the " +"system where in the filesystem to relocate the core dump on reboot." +msgstr "" + +#. type: Plain text +#: documentation/content/en/articles/geom-class/_index.adoc:162 +msgid "" +"Writing kernel core dumps is slow and takes a long time so if you have lots " +"of memory (>256M) and lots of panics it could be frustrating to sit and wait " +"while it is done (twice - first to write it to swap, then to relocate it to " +"filesystem). It is convenient then to limit the amount of RAM the system " +"will use via a [.filename]#/boot/loader.conf# tunable:" +msgstr "" + +#. type: delimited block . 4 +#: documentation/content/en/articles/geom-class/_index.adoc:166 +#, no-wrap +msgid " hw.physmem=\"256M\"\n" +msgstr "" + +#. type: Plain text +#: documentation/content/en/articles/geom-class/_index.adoc:169 +msgid "" +"If the panics are frequent and filesystems large (or you simply do not trust " +"softupdates+background fsck) it is advisable to turn background fsck off via " +"[.filename]#/etc/rc.conf# variable:" +msgstr "" + +#. type: delimited block . 4 +#: documentation/content/en/articles/geom-class/_index.adoc:173 +#, no-wrap +msgid " background_fsck=\"NO\"\n" +msgstr "" + +#. type: Plain text +#: documentation/content/en/articles/geom-class/_index.adoc:178 +msgid "" +"This way, the filesystems will always get checked when needed. Note that " +"with background fsck, a new panic could happen while it is checking the " +"disks. Again, the safest way is not to have many local filesystems by using " +"another computer as an NFS server." +msgstr "" + +#. type: Title === +#: documentation/content/en/articles/geom-class/_index.adoc:180 +#, no-wrap +msgid "Starting the Project" +msgstr "" + +#. type: Plain text +#: documentation/content/en/articles/geom-class/_index.adoc:184 +msgid "" +"For the purpose of creating a new GEOM class, an empty subdirectory has to " +"be created under an arbitrary user-accessible directory. You do not have to " +"create the module directory under [.filename]#/usr/src#." +msgstr "" + +#. type: Title === +#: documentation/content/en/articles/geom-class/_index.adoc:186 +#, no-wrap +msgid "The Makefile" +msgstr "" + +#. type: Plain text +#: documentation/content/en/articles/geom-class/_index.adoc:189 +msgid "" +"It is good practice to create [.filename]#Makefiles# for every nontrivial " +"coding project, which of course includes kernel modules." +msgstr "" + +#. type: Plain text +#: documentation/content/en/articles/geom-class/_index.adoc:192 +msgid "" +"Creating the [.filename]#Makefile# is simple thanks to an extensive set of " +"helper routines provided by the system. In short, here is how a minimal [." +"filename]#Makefile# looks for a kernel module:" +msgstr "" + +#. type: delimited block . 4 +#: documentation/content/en/articles/geom-class/_index.adoc:197 +#, no-wrap +msgid "" +"SRCS=g_journal.c\n" +"KMOD=geom_journal\n" +msgstr "" + +#. type: delimited block . 4 +#: documentation/content/en/articles/geom-class/_index.adoc:199 +#, no-wrap +msgid ".include <bsd.kmod.mk>\n" +msgstr "" + +#. type: Plain text +#: documentation/content/en/articles/geom-class/_index.adoc:203 +msgid "" +"This [.filename]#Makefile# (with changed filenames) will do for any kernel " +"module, and a GEOM class can reside in just one kernel module. If more than " +"one file is required, list it in the `SRCS` variable, separated with " +"whitespace from other filenames." +msgstr "" + +#. type: Title == +#: documentation/content/en/articles/geom-class/_index.adoc:205 +#, no-wrap +msgid "On FreeBSD Kernel Programming" +msgstr "" + +#. type: Title === +#: documentation/content/en/articles/geom-class/_index.adoc:208 +#, no-wrap +msgid "Memory Allocation" +msgstr "" + +#. type: Plain text +#: documentation/content/en/articles/geom-class/_index.adoc:213 +msgid "" +"See man:malloc[9]. Basic memory allocation is only slightly different than " +"its userland equivalent. Most notably, `malloc`() and `free`() accept " +"additional parameters as is described in the man page." +msgstr "" + +#. type: Plain text +#: documentation/content/en/articles/geom-class/_index.adoc:215 +msgid "" +"A \"malloc type\" must be declared in the declaration section of a source " +"file, like this:" +msgstr "" + +#. type: delimited block . 4 +#: documentation/content/en/articles/geom-class/_index.adoc:219 +#, no-wrap +msgid " static MALLOC_DEFINE(M_GJOURNAL, \"gjournal data\", \"GEOM_JOURNAL Data\");\n" +msgstr "" + +#. type: Plain text +#: documentation/content/en/articles/geom-class/_index.adoc:222 +msgid "" +"To use this macro, [.filename]#sys/param.h#, [.filename]#sys/kernel.h# and [." +"filename]#sys/malloc.h# headers must be included." +msgstr "" + +#. type: Plain text +#: documentation/content/en/articles/geom-class/_index.adoc:225 +msgid "" +"There is another mechanism for allocating memory, the UMA (Universal Memory " +"Allocator). See man:uma[9] for details, but it is a special type of " +"allocator mainly used for speedy allocation of lists comprised of same-sized " +"items (for example, dynamic arrays of structs)." +msgstr "" + +#. type: Title === +#: documentation/content/en/articles/geom-class/_index.adoc:227 +#, no-wrap +msgid "Lists and Queues" +msgstr "" + +#. type: Plain text +#: documentation/content/en/articles/geom-class/_index.adoc:234 +msgid "" +"See man:queue[3]. There are a LOT of cases when a list of things needs to " +"be maintained. Fortunately, this data structure is implemented (in several " +"ways) by C macros included in the system. The most used list type is TAILQ " +"because it is the most flexible. It is also the one with largest memory " +"requirements (its elements are doubly-linked) and also the slowest (although " +"the speed variation is on the order of several CPU instructions more, so it " +"should not be taken seriously)." +msgstr "" + +#. type: Plain text +#: documentation/content/en/articles/geom-class/_index.adoc:236 +msgid "" +"If data retrieval speed is very important, see man:tree[3] and man:" +"hashinit[9]." +msgstr "" + +#. type: Title === +#: documentation/content/en/articles/geom-class/_index.adoc:238 +#, no-wrap +msgid "BIOs" +msgstr "" + +#. type: Plain text +#: documentation/content/en/articles/geom-class/_index.adoc:242 +msgid "" +"Structure `bio` is used for any and all Input/Output operations concerning " +"GEOM. It basically contains information about what device ('provider') " +"should satisfy the request, request type, offset, length, pointer to a " +"buffer, and a bunch of \"user-specific\" flags and fields that can help " +"implement various hacks." +msgstr "" + +#. type: Plain text +#: documentation/content/en/articles/geom-class/_index.adoc:246 +msgid "" +"The important thing here is that ``bio``s are handled asynchronously. That " +"means that, in most parts of the code, there is no analogue to userland's " +"man:read[2] and man:write[2] calls that do not return until a request is " +"done. Rather, a developer-supplied function is called as a notification " +"when the request gets completed (or results in error)." +msgstr "" + +#. type: Plain text +#: documentation/content/en/articles/geom-class/_index.adoc:250 +msgid "" +"The asynchronous programming model (also called \"event-driven\") is " +"somewhat harder than the much more used imperative one used in userland (at " +"least it takes a while to get used to it). In some cases the helper " +"routines `g_write_data`() and `g_read_data`() can be used, but __not " +"always__. In particular, they cannot be used when a mutex is held; for " +"example, the GEOM topology mutex or the internal mutex held during the `." +"start`() and `.stop`() functions." +msgstr "" + +#. type: Title == +#: documentation/content/en/articles/geom-class/_index.adoc:252 +#, no-wrap +msgid "On GEOM Programming" +msgstr "" + +#. type: Title === +#: documentation/content/en/articles/geom-class/_index.adoc:255 +#, no-wrap +msgid "Ggate" +msgstr "" + +#. type: Plain text +#: documentation/content/en/articles/geom-class/_index.adoc:259 +msgid "" +"If maximum performance is not needed, a much simpler way of making a data " +"transformation is to implement it in userland via the ggate (GEOM gate) " +"facility. Unfortunately, there is no easy way to convert between, or even " +"share code between the two approaches." +msgstr "" + +#. type: Title === +#: documentation/content/en/articles/geom-class/_index.adoc:261 +#, no-wrap +msgid "GEOM Class" +msgstr "" + +#. type: Plain text +#: documentation/content/en/articles/geom-class/_index.adoc:266 +msgid "" +"GEOM classes are transformations on the data. These transformations can be " +"combined in a tree-like fashion. Instances of GEOM classes are called " +"__geoms__." +msgstr "" + +#. type: Plain text +#: documentation/content/en/articles/geom-class/_index.adoc:268 +msgid "" +"Each GEOM class has several \"class methods\" that get called when there is " +"no geom instance available (or they are simply not bound to a single " +"instance):" +msgstr "" + +#. type: Plain text +#: documentation/content/en/articles/geom-class/_index.adoc:270 +msgid "" +"`.init` is called when GEOM becomes aware of a GEOM class (when the kernel " +"module gets loaded.)" +msgstr "" + +#. type: Plain text +#: documentation/content/en/articles/geom-class/_index.adoc:271 +msgid "" +"`.fini` gets called when GEOM abandons the class (when the module gets " +"unloaded)" +msgstr "" + +#. type: Plain text +#: documentation/content/en/articles/geom-class/_index.adoc:272 +msgid "" +"`.taste` is called next, once for each provider the system has available. If " +"applicable, this function will usually create and start a geom instance." +msgstr "" + +#. type: Plain text +#: documentation/content/en/articles/geom-class/_index.adoc:273 +msgid "`.destroy_geom` is called when the geom should be disbanded" +msgstr "" + +#. type: Plain text +#: documentation/content/en/articles/geom-class/_index.adoc:274 +msgid "" +"`.ctlconf` is called when user requests reconfiguration of existing geom" +msgstr "" + +#. type: Plain text +#: documentation/content/en/articles/geom-class/_index.adoc:276 +msgid "" +"Also defined are the GEOM event functions, which will get copied to the geom " +"instance." +msgstr "" + +#. type: Plain text +#: documentation/content/en/articles/geom-class/_index.adoc:278 +msgid "" +"Field `.geom` in the `g_class` structure is a LIST of geoms instantiated " +"from the class." +msgstr "" + +#. type: Plain text +#: documentation/content/en/articles/geom-class/_index.adoc:280 +msgid "These functions are called from the g_event kernel thread." +msgstr "" + +#. type: Title === +#: documentation/content/en/articles/geom-class/_index.adoc:282 +#, no-wrap +msgid "Softc" +msgstr "" + +#. type: Plain text +#: documentation/content/en/articles/geom-class/_index.adoc:288 +msgid "" +"The name \"softc\" is a legacy term for \"driver private data\". The name " +"most probably comes from the archaic term \"software control block\". In " +"GEOM, it is a structure (more precise: pointer to a structure) that can be " +"attached to a geom instance to hold whatever data is private to the geom " +"instance. Most GEOM classes have the following members:" +msgstr "" + +#. type: Plain text +#: documentation/content/en/articles/geom-class/_index.adoc:290 +msgid "`struct g_provider *provider` : The \"provider\" this geom instantiates" +msgstr "" + +#. type: Plain text +#: documentation/content/en/articles/geom-class/_index.adoc:291 +msgid "`uint16_t n_disks` : Number of consumer this geom consumes" +msgstr "" + +#. type: Plain text +#: documentation/content/en/articles/geom-class/_index.adoc:292 +msgid "" +"`struct g_consumer \\**disks` : Array of `struct g_consumer*`. (It is not " +"possible to use just single indirection because struct g_consumer* are " +"created on our behalf by GEOM)." +msgstr "" + +#. type: Plain text +#: documentation/content/en/articles/geom-class/_index.adoc:295 +msgid "" +"The `softc` structure contains all the state of geom instance. Every geom " +"instance has its own softc." +msgstr "" + +#. type: Title === +#: documentation/content/en/articles/geom-class/_index.adoc:297 +#, no-wrap +msgid "Metadata" +msgstr "" + +#. type: Plain text +#: documentation/content/en/articles/geom-class/_index.adoc:300 +msgid "" +"Format of metadata is more-or-less class-dependent, but MUST start with:" +msgstr "" + +#. type: Plain text +#: documentation/content/en/articles/geom-class/_index.adoc:302 +msgid "16 byte buffer for null-terminated signature (usually the class name)" +msgstr "" + +#. type: Plain text +#: documentation/content/en/articles/geom-class/_index.adoc:303 +msgid "uint32 version ID" +msgstr "" + +#. type: Plain text +#: documentation/content/en/articles/geom-class/_index.adoc:305 +msgid "" +"It is assumed that geom classes know how to handle metadata with version " +"ID's lower than theirs." +msgstr "" + +#. type: Plain text +#: documentation/content/en/articles/geom-class/_index.adoc:307 +msgid "" +"Metadata is located in the last sector of the provider (and thus must fit in " +"it)." +msgstr "" + +#. type: Plain text +#: documentation/content/en/articles/geom-class/_index.adoc:309 +msgid "" +"(All this is implementation-dependent but all existing code works like that, " +"and it is supported by libraries.)" +msgstr "" + +#. type: Title === +#: documentation/content/en/articles/geom-class/_index.adoc:311 +#, no-wrap +msgid "Labeling/creating a GEOM" +msgstr "" + +#. type: Plain text +#: documentation/content/en/articles/geom-class/_index.adoc:314 +msgid "The sequence of events is:" +msgstr "" + +#. type: Plain text +#: documentation/content/en/articles/geom-class/_index.adoc:316 +msgid "user calls man:geom[8] utility (or one of its hardlinked friends)" +msgstr "" + +#. type: Plain text +#: documentation/content/en/articles/geom-class/_index.adoc:317 +msgid "" +"the utility figures out which geom class it is supposed to handle and " +"searches for [.filename]#geom_CLASSNAME.so# library (usually in [.filename]#/" +"lib/geom#)." +msgstr "" + +#. type: Plain text +#: documentation/content/en/articles/geom-class/_index.adoc:318 +msgid "" +"it man:dlopen[3]-s the library, extracts the definitions of command-line " +"parameters and helper functions." +msgstr "" + +#. type: Plain text +#: documentation/content/en/articles/geom-class/_index.adoc:320 +msgid "In the case of creating/labeling a new geom, this is what happens:" +msgstr "" + +#. type: Plain text +#: documentation/content/en/articles/geom-class/_index.adoc:322 +msgid "" +"man:geom[8] looks in the command-line argument for the command (usually " +"`label`), and calls a helper function." +msgstr "" + +#. type: Plain text +#: documentation/content/en/articles/geom-class/_index.adoc:323 +msgid "" +"The helper function checks parameters and gathers metadata, which it " +"proceeds to write to all concerned providers." +msgstr "" + +#. type: Plain text +#: documentation/content/en/articles/geom-class/_index.adoc:324 +msgid "" +"This \"spoils\" existing geoms (if any) and initializes a new round of " +"\"tasting\" of the providers. The intended geom class recognizes the " +"metadata and brings the geom up." +msgstr "" + +#. type: Plain text +#: documentation/content/en/articles/geom-class/_index.adoc:326 +msgid "" +"(The above sequence of events is implementation-dependent but all existing " +"code works like that, and it is supported by libraries.)" +msgstr "" + +#. type: Title === +#: documentation/content/en/articles/geom-class/_index.adoc:328 +#, no-wrap +msgid "GEOM Command Structure" +msgstr "" + +#. type: Plain text +#: documentation/content/en/articles/geom-class/_index.adoc:332 +msgid "" +"The helper [.filename]#geom_CLASSNAME.so# library exports `class_commands` " +"structure, which is an array of `struct g_command` elements. Commands are " +"of uniform format and look like:" +msgstr "" + +#. type: delimited block . 4 +#: documentation/content/en/articles/geom-class/_index.adoc:336 +#, no-wrap +msgid " verb [-options] geomname [other]\n" +msgstr "" + +#. type: Plain text +#: documentation/content/en/articles/geom-class/_index.adoc:339 +msgid "Common verbs are:" +msgstr "" + +#. type: Plain text +#: documentation/content/en/articles/geom-class/_index.adoc:341 +msgid "" +"label - to write metadata to devices so they can be recognized at tasting " +"and brought up in geoms" +msgstr "" + +#. type: Plain text +#: documentation/content/en/articles/geom-class/_index.adoc:342 +msgid "destroy - to destroy metadata, so the geoms get destroyed" +msgstr "" + +#. type: Plain text +#: documentation/content/en/articles/geom-class/_index.adoc:344 +msgid "Common options are:" +msgstr "" + +#. type: Plain text +#: documentation/content/en/articles/geom-class/_index.adoc:346 +msgid "`-v` : be verbose" +msgstr "" + +#. type: Plain text +#: documentation/content/en/articles/geom-class/_index.adoc:347 +msgid "`-f` : force" +msgstr "" + +#. type: Plain text +#: documentation/content/en/articles/geom-class/_index.adoc:351 +msgid "" +"Many actions, such as labeling and destroying metadata can be performed in " +"userland. For this, `struct g_command` provides field `gc_func` that can be " +"set to a function (in the same [.filename]#.so#) that will be called to " +"process a verb. If `gc_func` is NULL, the command will be passed to kernel " +"module, to `.ctlreq` function of the geom class." +msgstr "" + +#. type: Title === +#: documentation/content/en/articles/geom-class/_index.adoc:353 +#, no-wrap +msgid "Geoms" +msgstr "" + +#. type: Plain text +#: documentation/content/en/articles/geom-class/_index.adoc:357 +msgid "" +"Geoms are instances of GEOM classes. They have internal data (a softc " +"structure) and some functions with which they respond to external events." +msgstr "" + +#. type: Plain text +#: documentation/content/en/articles/geom-class/_index.adoc:359 +msgid "The event functions are:" +msgstr "" + +#. type: Plain text +#: documentation/content/en/articles/geom-class/_index.adoc:361 +msgid "`.access` : calculates permissions (read/write/exclusive)" +msgstr "" + +#. type: Plain text +#: documentation/content/en/articles/geom-class/_index.adoc:362 +msgid "`.dumpconf` : returns XML-formatted information about the geom" +msgstr "" + +#. type: Plain text +#: documentation/content/en/articles/geom-class/_index.adoc:363 +msgid "`.orphan` : called when some underlying provider gets disconnected" +msgstr "" + +#. type: Plain text +#: documentation/content/en/articles/geom-class/_index.adoc:364 +msgid "`.spoiled` : called when some underlying provider gets written to" +msgstr "" + +#. type: Plain text +#: documentation/content/en/articles/geom-class/_index.adoc:365 +msgid "`.start` : handles I/O" +msgstr "" + +#. type: Plain text +#: documentation/content/en/articles/geom-class/_index.adoc:367 +msgid "" +"These functions are called from the `g_down` kernel thread and there can be " +"no sleeping in this context, (see definition of sleeping elsewhere) which " +"limits what can be done quite a bit, but forces the handling to be fast." +msgstr "" + +#. type: Plain text +#: documentation/content/en/articles/geom-class/_index.adoc:369 +msgid "" +"Of these, the most important function for doing actual useful work is the `." +"start`() function, which is called when a BIO request arrives for a provider " +"managed by a instance of geom class." +msgstr "" + +#. type: Title === +#: documentation/content/en/articles/geom-class/_index.adoc:371 +#, no-wrap +msgid "GEOM Threads" +msgstr "" + +#. type: Plain text +#: documentation/content/en/articles/geom-class/_index.adoc:374 +msgid "There are three kernel threads created and run by the GEOM framework:" +msgstr "" + +#. type: Plain text +#: documentation/content/en/articles/geom-class/_index.adoc:376 +msgid "" +"`g_down` : Handles requests coming from high-level entities (such as a " +"userland request) on the way to physical devices" +msgstr "" + +#. type: Plain text +#: documentation/content/en/articles/geom-class/_index.adoc:377 +msgid "" +"`g_up` : Handles responses from device drivers to requests made by higher-" +"level entities" +msgstr "" + +#. type: Plain text +#: documentation/content/en/articles/geom-class/_index.adoc:378 +msgid "" +"`g_event` : Handles all other cases: creation of geom instances, access " +"counting, \"spoil\" events, etc." +msgstr "" + +#. type: Plain text +#: documentation/content/en/articles/geom-class/_index.adoc:380 +msgid "" +"When a user process issues \"read data X at offset Y of a file\" request, " +"this is what happens:" +msgstr "" + +#. type: Plain text +#: documentation/content/en/articles/geom-class/_index.adoc:382 +msgid "" +"The filesystem converts the request into a struct bio instance and passes it " +"to the GEOM subsystem. It knows what geom instance should handle it because " +"filesystems are hosted directly on a geom instance." +msgstr "" + +#. type: Plain text +#: documentation/content/en/articles/geom-class/_index.adoc:383 +msgid "" +"The request ends up as a call to the `.start`() function made on the g_down " +"thread and reaches the top-level geom instance." +msgstr "" + +#. type: Plain text +#: documentation/content/en/articles/geom-class/_index.adoc:384 +msgid "" +"This top-level geom instance (for example the partition slicer) determines " +"that the request should be routed to a lower-level instance (for example the " +"disk driver). It makes a copy of the bio request (bio requests _ALWAYS_ need " +"to be copied between instances, with `g_clone_bio`()!), modifies the data " +"offset and target provider fields and executes the copy with `g_io_request`()" +msgstr "" + +#. type: Plain text +#: documentation/content/en/articles/geom-class/_index.adoc:385 +msgid "" +"The disk driver gets the bio request also as a call to `.start`() on the " +"`g_down` thread. It talks to hardware, gets the data back, and calls " +"`g_io_deliver`() on the bio." +msgstr "" + +#. type: Plain text +#: documentation/content/en/articles/geom-class/_index.adoc:386 +msgid "" +"Now, the notification of bio completion \"bubbles up\" in the `g_up` thread. " +"First the partition slicer gets `.done`() called in the `g_up` thread, it " +"uses information stored in the bio to free the cloned `bio` structure (with " +"`g_destroy_bio`()) and calls `g_io_deliver`() on the original request." +msgstr "" + +#. type: Plain text +#: documentation/content/en/articles/geom-class/_index.adoc:387 +msgid "The filesystem gets the data and transfers it to userland." +msgstr "" + +#. type: Plain text +#: documentation/content/en/articles/geom-class/_index.adoc:389 +msgid "" +"See man:g_bio[9] man page for information how the data is passed back and " +"forth in the `bio` structure (note in particular the `bio_parent` and " +"`bio_children` fields and how they are handled)." +msgstr "" + +#. type: Plain text +#: documentation/content/en/articles/geom-class/_index.adoc:392 +msgid "" +"One important feature is: __THERE CAN BE NO SLEEPING IN G_UP AND G_DOWN " +"THREADS__. This means that none of the following things can be done in " +"those threads (the list is of course not complete, but only informative):" +msgstr "" + +#. type: Plain text +#: documentation/content/en/articles/geom-class/_index.adoc:394 +msgid "Calls to `msleep`() and `tsleep`(), obviously." +msgstr "" + +#. type: Plain text +#: documentation/content/en/articles/geom-class/_index.adoc:395 +msgid "" +"Calls to `g_write_data`() and `g_read_data`(), because these sleep between " +"passing the data to consumers and returning." +msgstr "" + +#. type: Plain text +#: documentation/content/en/articles/geom-class/_index.adoc:396 +msgid "Waiting for I/O." +msgstr "" + +#. type: Plain text +#: documentation/content/en/articles/geom-class/_index.adoc:397 +msgid "Calls to man:malloc[9] and `uma_zalloc`() with `M_WAITOK` flag set" +msgstr "" + +#. type: Plain text +#: documentation/content/en/articles/geom-class/_index.adoc:398 +msgid "sx and other sleepable locks" +msgstr "" + +#. type: Plain text +#: documentation/content/en/articles/geom-class/_index.adoc:402 +msgid "" +"This restriction is here to stop GEOM code clogging the I/O request path, " +"since sleeping is usually not time-bound and there can be no guarantees on " +"how long will it take (there are some other, more technical reasons also). " +"It also means that there is not much that can be done in those threads; for " +"example, almost any complex thing requires memory allocation. Fortunately, " +"there is a way out: creating additional kernel threads." +msgstr "" + +#. type: Title === +#: documentation/content/en/articles/geom-class/_index.adoc:404 +#, no-wrap +msgid "Kernel Threads for Use in GEOM Code" +msgstr "" + +#. type: Plain text +#: documentation/content/en/articles/geom-class/_index.adoc:407 +msgid "" +"Kernel threads are created with man:kthread_create[9] function, and they are " +"sort of similar to userland threads in behavior, only they cannot return to " +"caller to signify termination, but must call man:kthread_exit[9]." +msgstr "" + +#. type: Plain text +#: documentation/content/en/articles/geom-class/_index.adoc:410 +msgid "" +"In GEOM code, the usual use of threads is to offload processing of requests " +"from `g_down` thread (the `.start`() function). These threads look like " +"\"event handlers\": they have a linked list of event associated with them " +"(on which events can be posted by various functions in various threads so it " +"must be protected by a mutex), take the events from the list one by one and " +"process them in a big `switch`() statement." +msgstr "" + +#. type: Plain text +#: documentation/content/en/articles/geom-class/_index.adoc:415 +msgid "" +"The main benefit of using a thread to handle I/O requests is that it can " +"sleep when needed. Now, this sounds good, but should be carefully thought " +"out. Sleeping is well and very convenient but can very effectively destroy " +"performance of the geom transformation. Extremely performance-sensitive " +"classes probably should do all the work in `.start`() function call, taking " +"great care to handle out-of-memory and similar errors." +msgstr "" + +#. type: Plain text +#: documentation/content/en/articles/geom-class/_index.adoc:419 +msgid "" +"The other benefit of having a event-handler thread like that is to serialize " +"all the requests and responses coming from different geom threads into one " +"thread. This is also very convenient but can be slow. In most cases, " +"handling of `.done`() requests can be left to the `g_up` thread." +msgstr "" + +#. type: Plain text +#: documentation/content/en/articles/geom-class/_index.adoc:422 +msgid "" +"Mutexes in FreeBSD kernel (see man:mutex[9]) have one distinction from their " +"more common userland cousins - the code cannot sleep while holding a " +"mutex). If the code needs to sleep a lot, man:sx[9] locks may be more " +"appropriate. On the other hand, if you do almost everything in a single " +"thread, you may get away with no mutexes at all." +msgstr "" |