We've been doing a terrible job of performing XML validation in our
various API that parse XML with a corresponding schema (we started
with domains back in commit dd69a14f, v1.2.12, but didn't catch all
domain-related APIs, didn't document the use of the flag, and didn't
cover other XML). New APIs (like checkpoints) should do the validation
unconditionally, but it doesn't hurt to continue retrofitting existing
APIs to at least allow the option.

While there are many APIs that could be improved, this patch focuses
on wiring up a new snapshot XML creation flag through all the
hypervisors that support snapshots, as well as exposing it in 'virsh
snapshot-create'.  For 'virsh snapshot-create-as', we blindly set the
flag without a command-line option, since the XML we create from the
command line should generally always comply (note that validation
might cause failures where it used to succeed, such as if we tighten
the RNG to reject a name of '../\n'); but blindly passing the flag
means we also have to add in fallback code to disable validation if
the server is too old to understand the flag.
Signed-off-by: NEric Blake <eblake@redhat.com>
Acked-by: NPeter Krempa <pkrempa@redhat.com>

Since I was copying this text to form checkpoint XML and API
documentation, I might as well make improvements along the way. Most
of these changes are based on reviews of the checkpoint docs.

Among other things: grammar tweaks, point to a single source of
documentation rather than repeating verbosity, reword things for
easier legibility.
Signed-off-by: NEric Blake <eblake@redhat.com>
Reviewed-by: NDaniel P. Berrangé <berrange@redhat.com>

Based on recent list questions about the proposed addition of
virDomainCheckpointCreateXML(REDEFINE), it is worth adding some
clarification to the existing snapshot redefine documentation that is
serving as the basis for checkpoints.

Normal snapshot creation requires very few elements from the user XML
(libvirt can pick sane defaults for items that are omitted, and many
fields, including <domain>, are documented as readonly output fields
ignored on input, produced by drivers that track it). But during
REDEFINE, the API wants the complete XML produced by an earlier
virDomainSnapshotGetXMLDesc; as the domain definition has likely
changed since the snapshot was first created, libvirt is unable to
recreate a <domain> sub-element that matches the original output
representing the domain state at the time the snapshot was first
created. In fact, reverting without a <domain> sub-element is risky
enough that we had to add a FORCE flag for virDomainSnapshotRevert().
In short, we only support omitting domain for qemu because of
backwards-compatibility to snapshots created before 0.9.5 started
capturing <domain>; even though there are other drivers like vbox that
do not output <domain> because they have other reliable ways to
revert.

And based on the confusion caused when omitting <domain> from snapshot
XML, the initial design for checkpoints in later patches will make
<domain> a mandatory element during its REDEFINE.

[Side note: the fact that <domain> can appear in <domainsnapshot> is a
reason we cannot add a new API for a bulk listing or redefine of all
snapshots of a single domain in one XML call (for example, a 1M
<domain> XML * 16 snapshots explodes into 16M in a bulk form, which
gets difficult to send over RPC). Perhaps we could add a flag to
request that the <domain> sub-element be omitted on output, but such
output is no longer suitable for sane REDEFINE input.]
Signed-off-by: NEric Blake <eblake@redhat.com>
Reviewed-by: NDaniel P. Berrangé <berrange@redhat.com>

We copy-and-paste a lot of our docs, as evidenced by the number of
*GetXMLDesc() functions which had the same unusual indentation and
missing capital in the second sentence of the returns paragraph.
Signed-off-by: NEric Blake <eblake@redhat.com>

When using virDomainSnapshotCreateXML with the REDEFINE flag on
multiple snapshot metadata XML descriptions, we require that a child
cannot be redefined before its parent.  Since libvirt already tracks a
DAG, it is more convenient if we can ensure that
virDomainListAllSnapshots() and friends have a way to return data in
an order that we can directly reuse, rather than having to
post-process the data ourselves to reconstruct the DAG.

Add VIR_DOMAIN_SNAPSHOT_LIST_TOPOLOGICAL as our new guarantee (well, a
guarantee at the time of the API call conclusion; there's always a
possible TOCTTOU race where someone redefining snapshots in between
the API results and the client actually using the list might render
the list out-of-date). Four listing APIs are directly benefitted by
the new flag; additionally, since we document that the older racy
ListNames interfaces should be sized by using the same flags on their
Num counterparts, the Num interfaces must document when they accept
(and ignore) the flag.

We could have supported the new flag just for the ListAll APIs (to
discourage people from using the older racy Num/ListNames APIs), but
it feels weird to special-case this flag value as being applicable to
only a subset of the API while all other List-related flags are
trivially applicable to all 6.
Signed-off-by: NEric Blake <eblake@redhat.com>
Reviewed-by: NJán Tomko <jtomko@redhat.com>
Reviewed-by: NDaniel P. Berrangé <berrange@redhat.com>

Fix an incorrect @xmlDesc comment, as well as adding more details
about which XML element should be root.
Signed-off-by: NEric Blake <eblake@redhat.com>

Upcoming patches plan to introduce virDomainCheckpointPtr as a new
object for use in incremental backups, along with documentation on
how incremental backups differ from snapshots.  But first, we need
to rename any existing mention of a 'system checkpoint' to instead
be a 'full system snapshot', so that we aren't overloading
the term checkpoint.
Signed-off-by: NEric Blake <eblake@redhat.com>
Reviewed-by: NJohn Ferlan <jferlan@redhat.com>

Commit f609cb85 (0.9.5) introduced virDomainSnapshotGetXMLDesc()'s use
of @flags as a subset of virDomainXMLFlags, documenting that 2 of the
3 flags defined at the time would never be valid.  Later, commit
28f8dfdc (1.0.0) introduced a new flag, VIR_DOMAIN_XML_MIGRATABLE, but
did not adjust the snapshot documentation to declare it as invalid.
However, since the flag is not accepted as valid by any of the
drivers (remote is just passthrough; esx and vbox don't support flags;
qemu, test, and vz only support VIR_DOMAIN_XML_SECURE), and it is
unlikely that the domain state saved off during a snapshot creation
needs to be migration-friendly (as the snapshot is not the source of
a migration), it is easier to just define an explicit set of supported
flags directly related to the snapshot API rather than trying to
borrow from domain API, and risking confusion if even more domain
flags are added later (in fact, I have an upcoming patch that plans to
add a new flag to virDomainGetXMLDesc that makes no sense for
snapshots).

There is no API or ABI impact (since we purposefully used unsigned int
rather than an enum type in public API, and since the new flag name
carries the same value as the reused name).
Signed-off-by: NEric Blake <eblake@redhat.com>
Reviewed-by: NJohn Ferlan <jferlan@redhat.com>

Whenever we declare a new object the first member of the struct
has to be virObject (or any other member of that family). Now, up
until now we did not care about the name of the struct member.
But lets unify it so that we can do some checks at compile time
later.

The unified name is 'parent'.
Signed-off-by: NMichal Privoznik <mprivozn@redhat.com>
Reviewed-by: NErik Skultety <eskultet@redhat.com>
Reviewed-by: NDaniel P. Berrangé <berrange@redhat.com>

Seeing a log message saying 'flags=93' is ambiguous & confusing unless
you happen to know that libvirt always prints flags as hex.  Change our
debug messages so that they always add a '0x' prefix when printing flags,
and '0' prefix when printing mode. A few other misc places gain a '0x'
prefix in error messages too.
Signed-off-by: NDaniel P. Berrange <berrange@redhat.com>

The API docs for the various vir$OBJECTGetConnect functions
contain a warning

  WARNING: When writing libvirt bindings in other languages, do
  not use this function.  Instead, store the connection and
  the domain object together.

There is no reason why language bindings should not use this
method, and indeed the Perl, Python, and Go bindings all use
these methods.

This warning was originally added back in

  commit 3edb4bc9
  Author: Daniel Veillard <veillard@redhat.com>
  Date:   Tue Jul 24 15:32:55 2007 +0000

    * libvirt.spec.in NEWS docs/* po/*: preparing release 0.3.1
    * src/libvirt.c python/generator.py: some cleanup and warnings
      from Richard W.M. Jones

IIUC, the rational was that these APIs do not need to be
directly exposed to the non-C language, as the language
can expose the same concept itself by storing the original
virConnectPtr object alongside the virDomainPtr.  There's
no reason to mandate such an approach though - it is valid
for languages to expose this directly if that suits their
needs better.
Signed-off-by: NDaniel P. Berrange <berrange@redhat.com>

Signed-off-by: NPavel Hrdina <phrdina@redhat.com>

Signed-off-by: NPavel Hrdina <phrdina@redhat.com>

When creating a snapshot with _REUSE_EXTERNAL when the pre-created image
does not directly link to the current active layer libvirt would
re-detect the backing chain incorrectly and it would not match with
qemu's view. Since the configuration is an operator mistake, document
that only the top layer image gets inserted.

The error output of snapshot-revert should be more friendly.
There is no need to show virDomainRevertToSnapshot to user.
virReportError already includes __FUNCTION__ information in a
separate member of the struct, so repeating it in the message is
redundant and leads to situations where higher level code ends up
reporting the lower level name. We correctly converted the error
output making it more succinct and user-friendly.

Resolves: https://bugzilla.redhat.com/show_bug.cgi?id=1086726

Introduce a src/libvirt-domain-snapshot.c file to hold all the
methods related to the virDomainSnapshot type.