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After the VG lock is taken for vg_read, reread the mda_header
and compare the metadata text offset and checksum to what was
seen during label scan. If it is unchanged, then the metadata
has not changed since the label scan, and the metadata does not
need to be reread under the lock for command processing.
For commands that do not make changes (e.g. reporting), the
mda_header is reread and checked on one mda to decide if the
full metadata rereading can be skipped. For other commands
(e.g. modifying the vg) the mda_header is reread and checked
from all PVs. (These could probably just check one mda also.)
When reading metadata headers and text, use a new set
of flags to identify specific errors that are seen.
These will be used for more advanced repair in a
subsequent commit.
As we start refactoring the code to break dependencies (see doc/refactoring.txt),
I want us to use full paths in the includes (eg, #include "base/data-struct/list.h").
This makes it more obvious when we're breaking abstraction boundaries, eg, including a file in
metadata/ from base/
New label_scan function populates bcache for each device
on the system.
The two read paths are updated to get data from bcache.
The bcache is not yet used for writing. bcache blocks
for a device are invalidated when the device is written.
If there is sufficient space in the metadata area, align the next
metadata to a disk offset that is a multiple of 4096 bytes and
don't write it circularly. If it doesn't all fit at the end
of the metadata area, go back to the start and write it all there
contiguously.
If there is insufficient space to use the new stricter rules, revert to
the original behaviour, aligning on 512-byte boundaries wrapping around
the circular buffer as required.
Expand out the metadata wrapping calculations to prepare
to support a larger alignment.
The current alignment is 512 bytes so
(mdac_area_start + rlocn->offset) % alignment is zero.
Mark the first metadata area on each text format PV as MDA_PRIMARY.
Pass this information down to the device layer so that when
there are two metadata areas on a block device, we can easily
distinguish two independent streams of I/O.
Refactor the recent metadata-reading optimisation patches.
Remove the recently-added cache fields from struct labeller
and struct format_instance.
Instead, introduce struct lvmcache_vgsummary to wrap the VG information
that lvmcache holds and add the metadata size and checksum to it.
Allow this VG summary information to be looked up by metadata size +
checksum. Adjust the debug log messages to make it clear when this
shortcut has been successful.
(This changes the optimisation slightly, and might be extendable
further.)
Add struct cached_vg_fmtdata to format-specific vg_read calls to
preserve state alongside the VG across separate calls and indicate
if the details supplied match, avoiding the need to read and
process the VG metadata again.
Use similar logic as with text_vg_import_fd() and avoid repeated
parsing of same mda and its config tree for vgname_from_mda().
Remember last parsed vgname, vgid and creation_host in labeller
structure and if the metadata have the same size and checksum,
return this stored info.
TODO: The reuse of labeller struct is not ideal, some lvmcache API for
this functionality would be nicer.
The list of strings is used quite frequently and we'd like to reuse
this simple structure for report selection support too. Make it part
of libdevmapper for general reuse throughout the code.
This also simplifies the LVM code a bit since we don't need to
include and manage lvm-types.h anymore (the string list was the
only structure defined there).
Just to prevent accidental and improper use when reading the layout
from disk because of the already existing disk_areas_xl[0] lists
that are variable in size. We can read pv_header_extension only
after we know exactly where the lists end...
New tools with PV header extension support will read the extension
if it exists and it's not an error if it does not exist (so old PVs
will still work seamlessly with new tools).
Old tools without PV header extension support will just ignore any
extension.
As for the Embedding Area location information (its start and size),
there are actually two places where this is stored:
- PV header extension
- VG metadata
The VG metadata contains a copy of what's written in the PV header
extension about the Embedding Area location (NULL value is not copied):
physical_volumes {
pv0 {
id = "AkSSRf-difg-fCCZ-NjAN-qP49-1zzg-S0Fd4T"
device = "/dev/sda" # Hint only
status = ["ALLOCATABLE"]
flags = []
dev_size = 262144 # 128 Megabytes
pe_start = 67584
pe_count = 23 # 92 Megabytes
ea_start = 2048
ea_size = 65536 # 32 Megabytes
}
}
The new metadata fields are "ea_start" and "ea_size".
This is mostly useful when restoring the PV by using existing
metadata backups (e.g. pvcreate --restorefile ...).
New tools does not require these two fields to exist in VG metadata,
they're not compulsory. Therefore, reading old VG metadata which doesn't
contain any Embedding Area information will not end up with any kind
of error but only a debug message that the ea_start and ea_size values
were not found.
Old tools just ignore these extra fields in VG metadata.
PV header extension comes just beyond the existing PV header base:
PV header base (existing):
- uuid
- device size
- null-terminated list of Data Areas
- null-terminater list of MetaData Areas
PV header extension:
- extension version
- flags
- null-terminated list of Embedding Areas
This patch also adds "eas" (Embedding Areas) list to lvmcache (lvmcache_info)
and it also adds support for common operations on the list (just like for
already existing "das" - Data Areas list):
- lvmcache_add_ea
- lvmcache_update_eas
- lvmcache_foreach_ea
- lvmcache_del_eas
Also, add ea_start and ea_size to struct physical_volume for processing
PV Embedding Area location throughout the code (currently only one
Embedding Area is supported, though the definition on disk allows for
more if needed in the future...).
Also, define FMT_EAS format flag to mark that the format actually
supports Embedding Areas (currently format-text only).
We'd like to pass in mda_header to vgname_from_mda(). In order to
do this, we need to call raw_read_mda_header() from text_label.c,
_text_read(), which gets called from the label_read() path, and
peers into the metadata and update vginfo cache. We should check
the disable bit here, and if set, not peer into the vg metadata,
thus reducing the I/O to disk.
In the process, move vgname_from_mda() to layout.h, since the fn
only gets called from format_text code, and we need the mda_header
definition from the private layout.h.
Signed-off-by: Dave Wysochanski <dwysocha@redhat.com>
Adding a flag to the 'rlocn' structure in the mda header of the
text format allows us to flip a bit to ignore an area on disk that
stores the metadata via the text format specific mda_header.
This patch defines the flag and access functions to manage the flag.
Other patches will manage the ignore on a format-independent basis,
by using a flag in the metadata_area structure.
Signed-off-by: Dave Wysochanski <dwysocha@redhat.com>
Future patches will make use of a specific flag in the on-disk 'raw_locn'
structure to enable/disable metadata areas, and facilitate metadata
balancing.
Note that 'filler' is always set to '0' (see add_mda() - memset),
so use of this area as a non-zero flags field is a safe way to
provide future code features.
Signed-off-by: Dave Wysochanski <dwysocha@redhat.com>
Fix some memory leaks in error paths found by coverity.
Use C99 struct initialisers.
Move DEFS into configure.h.
Clean-ups to remove miscellaneous compiler warnings.
