shaba/lvm2
1
0
Fork 0
mirror of git://sourceware.org/git/lvm2.git synced 2024-12-30 17:18:21 +03:00
Code Releases Activity

filters: clarify some parts of md filter

Browse Source 
Rename some functions to be consistent with the return values,
and add some comments about how it works.
This commit is contained in:
David Teigland 2018-05-22 14:07:13 -05:00
parent 3c9ed33f83
commit 61583281e5
1 changed files with 78 additions and 11 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

89
lib/filters/filter-md.c
View File

@ -20,13 +20,77 @@
#define MSG_SKIPPING "%s: Skipping md component device"
static int _ignore_md(struct device *dev, int full)
/*
* The purpose of these functions is to ignore md component devices,
* e.g. if /dev/md0 is a raid1 composed of /dev/loop0 and /dev/loop1,
* lvm wants to deal with md0 and ignore loop0 and loop1. md0 should
* pass the filter, and loop0,loop1 should not pass the filter so lvm
* will ignore them.
*
* (This is assuming lvm.conf md_component_detection=1.)
*
* If lvm does *not* ignore the components, then lvm will read lvm
* labels from the md dev and from the component devs, and will see
* them all as duplicates of each other. LVM duplicate resolution
* will then kick in and keep the md dev around to use and ignore
* the components.
*
* It is better to exclude the components as early as possible during
* lvm processing, ideally before lvm even looks for labels on the
* components, so that duplicate resolution can be avoided. There are
* a number of ways that md components can be excluded earlier than
* the duplicate resolution phase:
*
* - When external_device_info_source="udev", lvm discovers a device is
* an md component by asking udev during the initial filtering phase.
* However, lvm's default is to not use udev for this. The
* alternative is "native" detection in which lvm tries to detect
* md components itself.
*
* - When using native detection, lvm's md filter looks for the md
* superblock at the start of devices. It will see the md superblock
* on the components, exclude them in the md filter, and avoid
* handling them later in duplicate resolution.
*
* - When using native detection, lvm's md filter will not detect
* components when the md device has an older superblock version that
* places the superblock at the end of the device. This case will
* fall back to duplicate resolution to exclude components.
*
* A variation of the description above occurs for lvm commands that
* intend to create new PVs on devices (pvcreate, vgcreate, vgextend).
* For these commands, the native md filter also reads the end of all
* devices to check for the odd md superblocks.
*
* (The reason that external_device_info_source is not set to udev by
* default is that there have be issues with udev not being promptly
* or reliably updated about md state changes, causing the udev info
* that lvm uses to be occasionally wrong.)
*/
/*
* Returns 0 if:
* the device is an md component and it should be ignored.
*
* Returns 1 if:
* the device is not md component and should not be ignored.
*
* The actual md device will pass this filter and should be used,
* it is the md component devices that we are trying to exclude
* that will not pass.
*/
static int _passes_md_filter(struct device *dev, int full)
{
int ret;
/*
* When md_component_dectection=0, don't even try to skip md
* components.
*/
if (!md_filtering())
return 1;
ret = dev_is_md(dev, NULL, full);
if (ret == -EAGAIN) {
@ -36,6 +100,9 @@ static int _ignore_md(struct device *dev, int full)
return 1;
}
if (ret == 0)
return 1;
if (ret == 1) {
if (dev->ext.src == DEV_EXT_NONE)
log_debug_devs(MSG_SKIPPING, dev_name(dev));
@ -54,16 +121,16 @@ static int _ignore_md(struct device *dev, int full)
return 1;
}
static int _ignore_md_lite(struct dev_filter *f __attribute__((unused)),
struct device *dev)
static int _passes_md_filter_lite(struct dev_filter *f __attribute__((unused)),
struct device *dev)
{
return _ignore_md(dev, 0);
return _passes_md_filter(dev, 0);
}
static int _ignore_md_full(struct dev_filter *f __attribute__((unused)),
struct device *dev)
static int _passes_md_filter_full(struct dev_filter *f __attribute__((unused)),
struct device *dev)
{
return _ignore_md(dev, 1);
return _passes_md_filter(dev, 1);
}
static void _destroy(struct dev_filter *f)
@ -91,9 +158,9 @@ struct dev_filter *md_filter_create(struct cmd_context *cmd, struct dev_types *d
*/
if (cmd->use_full_md_check)
f->passes_filter = _ignore_md_full;
f->passes_filter = _passes_md_filter_full;
else
f->passes_filter = _ignore_md_lite;
f->passes_filter = _passes_md_filter_lite;
f->destroy = _destroy;
f->use_count = 0;