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diff --git a/share/man/man9/sysctl_ctx_init.9 b/share/man/man9/sysctl_ctx_init.9 new file mode 100644 index 0000000..b3c0d3b --- /dev/null +++ b/share/man/man9/sysctl_ctx_init.9 @@ -0,0 +1,247 @@ +.\" +.\" Copyright (c) 2000, Andrzej Bialecki <abial@FreeBSD.org> +.\" All rights reserved. +.\" +.\" Redistribution and use in source and binary forms, with or without +.\" modification, are permitted provided that the following conditions +.\" are met: +.\" 1. Redistributions of source code must retain the above copyright +.\" notice, this list of conditions and the following disclaimer. +.\" 2. Redistributions in binary form must reproduce the above copyright +.\" notice, this list of conditions and the following disclaimer in the +.\" documentation and/or other materials provided with the distribution. +.\" 3. The name of the author may not be used to endorse or promote products +.\" derived from this software without specific prior written permission. +.\" +.\" THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND +.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE +.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE +.\" ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE +.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL +.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS +.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) +.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT +.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY +.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF +.\" SUCH DAMAGE. +.\" +.\" $FreeBSD$ +.\" +.Dd July 15, 2000 +.Dt SYSCTL_CTX_INIT 9 +.Os +.Sh NAME +.Nm sysctl_ctx_init , +.Nm sysctl_ctx_free , +.Nm sysctl_ctx_entry_add , +.Nm sysctl_ctx_entry_find , +.Nm sysctl_ctx_entry_del +.Nd "sysctl context for managing dynamically created sysctl oids" +.Sh SYNOPSIS +.In sys/types.h +.In sys/sysctl.h +.Ft int +.Fo sysctl_ctx_init +.Fa "struct sysctl_ctx_list *clist" +.Fc +.Ft int +.Fo sysctl_ctx_free +.Fa "struct sysctl_ctx_list *clist" +.Fc +.Ft struct sysctl_ctx_entry * +.Fo sysctl_ctx_entry_add +.Fa "struct sysctl_ctx_list *clist" +.Fa "struct sysctl_oid *oidp" +.Fc +.Ft struct sysctl_ctx_entry * +.Fo sysctl_ctx_entry_find +.Fa "struct sysctl_ctx_list *clist" +.Fa "struct sysctl_oid *oidp" +.Fc +.Ft int +.Fo sysctl_ctx_entry_del +.Fa "struct sysctl_ctx_list *clist" +.Fa "struct sysctl_oid *oidp" +.Fc +.Sh DESCRIPTION +These functions provide an interface +for managing dynamically created oids. +The sysctl context is responsible for keeping track of created oids, +as well as their proper removal when needed. +It adds a simple transactional aspect to oid removal operations; +i.e., if a removal operation fails part way, +it is possible to roll back the sysctl tree +to its previous state. +.Pp +The +.Fn sysctl_ctx_init +function initializes a sysctl context. +The +.Fa clist +argument must point to an already allocated variable. +A context +.Em must +be initialized before use. +Once it is initialized, +a pointer to the context can be passed as an argument to all the +.Fa SYSCTL_ADD_* +macros (see +.Xr sysctl_add_oid 9 ) , +and it will be updated with entries pointing to newly created oids. +.Pp +Internally, the context is represented as a +.Xr queue 3 +TAILQ linked list. +The list consists of +.Li struct sysctl_ctx_entry +entries: +.Bd -literal -offset indent +struct sysctl_ctx_entry { + struct sysctl_oid *entry; + TAILQ_ENTRY(sysctl_ctx_entry) link; +}; + +TAILQ_HEAD(sysctl_ctx_list, sysctl_ctx_entry); +.Ed +.Pp +Each context entry points to one dynamic oid that it manages. +Newly created oids are always inserted in the front of the list. +.Pp +The +.Fn sysctl_ctx_free +function removes the context and associated oids it manages. +If the function completes successfully, +all managed oids have been unregistered +(removed from the tree) +and freed, +together with all their allocated memory, +and the entries of the context have been freed as well. +.Pp +The removal operation is performed in two steps. +First, for each context entry, the function +.Xr sysctl_remove_oid 9 +is executed, with parameter +.Fa del +set to 0, which inhibits the freeing of resources. +If there are no errors during this step, +.Fn sysctl_ctx_free +proceeds to the next step. +If the first step fails, +all unregistered oids associated with the context are registered again. +.Pp +.Em Note : +in most cases, the programmer specifies +.Dv OID_AUTO +as the oid number when creating an oid. +However, during registration of the oid in the tree, +this number is changed to the first available number +greater than or equal to +.Dv CTL_AUTO_START . +If the first step of context deletion fails, +re-registration of the oid does not change the already assigned oid number +(which is different from OID_AUTO). +This ensures that re-registered entries +maintain their original positions in the tree. +.Pp +The second step actually performs the deletion of the dynamic oids. +.Xr sysctl_remove_oid 9 +iterates through the context list, +starting from beginning (i.e., the newest entries). +.Em Important : +this time, the function not only deletes the oids from the tree, +but also frees their memory (provided that oid_refcnt == 0), +as well as the memory of all context entries. +.Pp +The +.Fn sysctl_ctx_entry_add +function allows the addition of an existing dynamic oid to a context. +.Pp +The +.Fn sysctl_ctx_entry_del +function removes an entry from the context. +.Em Important : +in this case, only the corresponding +.Li struct sysctl_ctx_entry +is freed, but the +.Fa oidp +pointer remains intact. +Thereafter, the programmer is responsible for managing the resources +allocated to this oid. +.Pp +The +.Fn sysctl_ctx_entry_find +function searches for a given +.Fa oidp +within a context list, +either returning a pointer to the +.Fa struct sysctl_ctx_entry +found, +or +.Dv NULL . +.Sh EXAMPLES +The following is an example of how to create a new top-level category +and how to hook up another subtree to an existing static node. +This example uses contexts to keep track of the oids. +.Bd -literal +#include <sys/sysctl.h> + ... +struct sysctl_ctx_list clist; +struct sysctl_oid *oidp; +int a_int; +const char *string = "dynamic sysctl"; + ... + +sysctl_ctx_init(&clist); +oidp = SYSCTL_ADD_NODE(&clist, SYSCTL_STATIC_CHILDREN(/* tree top */), + OID_AUTO, "newtree", CTLFLAG_RW, 0, "new top level tree"); +oidp = SYSCTL_ADD_INT(&clist, SYSCTL_CHILDREN(oidp), + OID_AUTO, "newint", CTLFLAG_RW, &a_int, 0, "new int leaf"); + ... +oidp = SYSCTL_ADD_NODE(&clist, SYSCTL_STATIC_CHILDREN(_debug), + OID_AUTO, "newtree", CTLFLAG_RW, 0, "new tree under debug"); +oidp = SYSCTL_ADD_STRING(&clist, SYSCTL_CHILDREN(oidp), + OID_AUTO, "newstring", CTLFLAG_RD, string, 0, "new string leaf"); + ... +/* Now we can free up the oids */ +if (sysctl_ctx_free(&clist)) { + printf("can't free this context - other oids depend on it"); + return (ENOTEMPTY); +} else { + printf("Success!\\n"); + return (0); +} +.Ed +.Pp +This example creates the following subtrees: +.Bd -literal -offset indent +debug.newtree.newstring +newtree.newint +.Ed +.Pp +Note that both trees are removed, and their resources freed, +through one +.Fn sysctl_ctx_free +call, which starts by freeing the newest entries (leaves) +and then proceeds to free the older entries (in this case the nodes). +.Sh SEE ALSO +.Xr queue 3 , +.Xr sysctl 8 , +.Xr sysctl 9 , +.Xr sysctl_add_oid 9 , +.Xr sysctl_remove_oid 9 +.Sh HISTORY +These functions first appeared in +.Fx 4.2 . +.Sh AUTHORS +.An Andrzej Bialecki Aq Mt abial@FreeBSD.org +.Sh BUGS +The current removal algorithm is somewhat heavy. +In the worst case, +all oids need to be unregistered, registered again, +and then unregistered and deleted. +However, the algorithm does guarantee transactional properties +for removal operations. +.Pp +All operations on contexts involve linked list traversal. +For this reason, +creation and removal of entries is relatively costly. |
