Add mda_locns_match() internal library function for mapping pv/device to VG mda.

A metadata_area is defined independent of the location.  One downside
is that there is no obvious mapping from a pv to an mda.  For a PV in
a VG, we need a way to start with a PV and end up with an MDA, if we
are to manage mdas starting with a device/pv.  This function provides
us a way to go down the list of PVs on a VG, and identify which ones
match a particular PV.

I'm not entirely happy with this approach, but it does fit into the
existing structures in a reasonable way.

An alternative solution might be to refactor the VG - PV interface such
that mdas are a list tied to a PV.  However, this seemed a bit tricky since
a PV does not come into existence until after the list of mdas is
constructed (see _vg_read() - we create a 'fid' and attach mdas to it,
then we go through them and attach pvs).

Signed-off-by: Dave Wysochanski <dwysocha@redhat.com>
Reviewed-by: Alasdair G Kergon <agk@redhat.com>

diff --git a/lib/format_text/format-text.c b/lib/format_text/format-text.c
index d4c6a749338d39f78d4559ade6a304bcc118a3b3..af33e572316690d6c5f63c69885922966be9eaa3 100644 (file)
--- a/lib/format_text/format-text.c
+++ b/lib/format_text/format-text.c
@@ -121,6 +121,20 @@ static int _mda_in_vg_raw(struct format_instance *fid __attribute((unused)),
        return 0;
 }
 
+static unsigned _mda_locns_match_raw(struct metadata_area *mda1,
+                                    struct metadata_area *mda2)
+{
+       struct mda_context *mda1c = (struct mda_context *) mda1->metadata_locn;
+       struct mda_context *mda2c = (struct mda_context *) mda2->metadata_locn;
+
+       if ((mda1c->area.dev == mda2c->area.dev) &&
+           (mda1c->area.start == mda2c->area.start) &&
+           (mda1c->area.size == mda2c->area.size))
+               return 1;
+
+       return 0;
+}
+
 /*
  * For circular region between region_start and region_start + region_size,
  * back up one SECTOR_SIZE from 'region_ptr' and return the value.
@@ -1732,6 +1746,7 @@ static struct metadata_area_ops _metadata_text_raw_ops = {
        .mda_total_sectors = _mda_total_sectors_raw,
        .mda_in_vg = _mda_in_vg_raw,
        .pv_analyze_mda = _pv_analyze_mda_raw,
+       .mda_locns_match = _mda_locns_match_raw
 };
 
 /* pvmetadatasize in sectors */

diff --git a/lib/metadata/metadata.c b/lib/metadata/metadata.c
index 891674d10d5fbca7324a0d3976aa383425788e3f..d59df0366c91c90120475ee6393711eafb242960 100644 (file)
--- a/lib/metadata/metadata.c
+++ b/lib/metadata/metadata.c
@@ -3855,6 +3855,36 @@ uint32_t pv_pe_alloc_count(const struct physical_volume *pv)
        return pv_field(pv, pe_alloc_count);
 }
 
+/*
+ * This function provides a way to answer the question on a format specific
+ * basis - does the format specfic context of these two metadata areas
+ * match?
+ *
+ * A metatdata_area is defined to be independent of the underlying context.
+ * This has the benefit that we can use the same abstraction to read disks
+ * (see _metadata_text_raw_ops) or files (see _metadata_text_file_ops).
+ * However, one downside is there is no format-independent way to determine
+ * whether a given metadata_area is attached to a specific device - in fact,
+ * it may not be attached to a device at all.
+ *
+ * Thus, LVM is structured such that an mda is not a member of struct
+ * physical_volume.  The location of the mda depends on whether
+ * the PV is in a volume group.  A PV not in a VG has an mda on the
+ * 'info->mda' list in lvmcache, while a PV in a VG has an mda on
+ * the vg->fid->metadata_areas list.  For further details, see _vg_read(),
+ * and the sequence of creating the format_instance with fid->metadata_areas
+ * list, as well as the construction of the VG, with list of PVs (comes
+ * after the construction of the fid and list of mdas).
+ */
+unsigned mda_locns_match(struct metadata_area *mda1, struct metadata_area *mda2)
+{
+       if (!mda1->ops->mda_locns_match || !mda2->ops->mda_locns_match ||
+           mda1->ops->mda_locns_match != mda2->ops->mda_locns_match)
+               return 0;
+
+       return mda1->ops->mda_locns_match(mda1, mda2);
+}
+
 unsigned mda_is_ignored(struct metadata_area *mda)
 {
        return (mda->flags & MDA_IGNORED);

diff --git a/lib/metadata/metadata.h b/lib/metadata/metadata.h
index 665ec99225a6bb35ce0236f478837d9e26947f13..7f132a85b04e7c4bf8a86267e167bfabdfcf931f 100644 (file)
--- a/lib/metadata/metadata.h
+++ b/lib/metadata/metadata.h
@@ -156,6 +156,12 @@ struct metadata_area_ops {
        int (*pv_analyze_mda) (const struct format_type * fmt,
                               struct metadata_area *mda);
 
+       /*
+        * Do these two metadata_areas match with respect to their underlying
+        * location?
+        */
+       unsigned (*mda_locns_match)(struct metadata_area *mda1,
+                                   struct metadata_area *mda2);
 };
 
 #define MDA_IGNORED 0x00000001
@@ -169,6 +175,7 @@ struct metadata_area {
 
 unsigned mda_is_ignored(struct metadata_area *mda);
 void mda_set_ignored(struct metadata_area *mda, int value);
+unsigned mda_locns_match(struct metadata_area *mda1, struct metadata_area *mda2);
 
 #define seg_pvseg(seg, s)      (seg)->areas[(s)].u.pv.pvseg
 #define seg_dev(seg, s)                (seg)->areas[(s)].u.pv.pvseg->pv->dev