Editing BC proc entries

{{UBC toc}}
This page describes proc interface of [[UBC]] subsystem.

== Old interface ==
The [[Proc/user_beancounters|old interface]] consisted of 2 (optionally 3) files:
; <code>/proc/user_beancounters</code>
: reveals an overall information about resource consumption of each beancounter in system; described [[Proc/user_beancounters|here]];
; <code>/proc/user_beancounters_sub</code>
: reveals information about all beancounters and sub-beancounters in system;
; <code>/proc/user_beancounters_debug</code>
: shows debugging information about each beancounter. Available if <code>CONFIG_UBC_DEBUG_KMEM</code> option is turned on. Information revealed includes the numbers of
:# objects charged from each slab;
:# pages charged;
:# vmalloc-ed pages;
:# page beancounters;
:# etc.

== New interface ==
In new interface only <code>user_beancounters</code> entry is left for compatibility with old tools. New entries reside in <code>/proc/bc</code> directory. This directory also contains subdirectories for each beancounter in the system. E.g.
<pre>
# ls /proc/bc/
0  ioacct_debug  resources
# vzctl  start 101
...
# ls /proc/bc
0  101  ioacct_debug  resources
# ls /proc/bc/101/
ioacct  kmem_debug  resources  vmaux
</pre>

All new entries that are in <code>/proc/bc</code> shows some overall information about BC subsystem, while entries in <code>/proc/bc/$BCID</code> show per-beancounter info.

=== Existing general entries ===
; <code>/proc/bc/resources</code>
: This entry looks like old <code>user_beancounters</code> entry but
# it doesn't contain “dummy” resources
# if new resource is added to BC it will appear in this entry only
; <code>/proc/bc/$BCID/resources</code>
: This entry shows the same as <code>bc/resources</code> does but for <code>$BCID</code> beancounter only.
; <code>/proc/bc/$BCID/vmaux</code>
: This entry shows auxiliary resources used in VM accounting.
; <code>/proc/bc/$BCID/kmem_debug</code>
: This entry is available with <code>CONFIG_UBC_DEBUG_KMEM</code> option set and shows per-beancounter info that was in <code>/proc/user_beancounters_debug</code> before.

=== Other entries ===
The following subsystems add their own entries in <code>/proc/bc</code> and <code>/proc/bc/$BCID</code>
* [[IO accounting]]

=== Kernel API ===
Subsystems may add its own entries in <code>/proc/bc</code> or <code>/proc/bc/$BCID</code>. To facilitate this the following API is used in BC sybsystem (declared in <code>include/ub/proc.h</code>).
; <code>struct proc_dir_entry *bc_proc_root</code>
: This is an entry that corresponds to <code>/proc/bc</code> directory. If a subsystem wishes to report some information that is not per-beancounter it may create entry using this as a parent.
; <code>struct bc_proc_entry;</code>
: This describes an entry that may show per-beancounter info. This looks like this:
<pre>
struct bc_proc_entry {
        char *name;
        int (*show)(struct seq_file *, void *);
        struct bc_proc_entry *next;
};
</pre>
* <code>name</code> is the entry name as it will appear in <code>/proc/bc/$BCID</code>
* <code>show</code> is a callback that is to fill info about particulat beancounter
; <code>void bc_register_proc_entry(struct bc_proc_entry *);</code>
: This call registers an entry that shows per-beancounter info.

The code that fills info about BC must look like this
<pre>
static int bc_my_show(struct seq_file *f, void *v)
{
        struct user_beancounter *ub;

        ub = seq_beancounter(f);
        /* dump info into f here */
        return 0;
}
...
static struct bc_proc_entry my_entry = {
        .name = "my_entry",
        .show = bc_my_show,
};

static int __init bc_my_init(void)
{
        bc_register_proc_entry(&my_entry);
        return 0;
}

late_initcall(bc_my_init);
</pre>
{{note|Due to limitations in <code>single_open</code> the <code>struct user_beancounter</code> pointer is not passed as <code>void *v</code> into showing function but must be obtained from <code>seq_file</code> with <code>seq_beancounter</code>}}