1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
|
/*
* solver3.h - The APT 3.0 solver
*
* Copyright (c) 2023 Julian Andres Klode
* Copyright (c) 2023 Canonical Ltd
*
* SPDX-License-Identifier: GPL-2.0+
*/
#include <vector>
#include <apt-pkg/configuration.h>
#include <apt-pkg/depcache.h>
#include <apt-pkg/pkgcache.h>
#include <apt-pkg/policy.h>
namespace APT
{
/*
* \brief APT 3.0 solver
*
* This is a simple solver focused on understandability and sensible results, it
* will not generally find all solutions to the problem but will try to find the best
* ones.
*
* It is a brute force solver with heuristics, conflicts learning, and 2**32 levels
* of backtracking.
*/
class Solver
{
enum class Decision : uint16_t;
enum class Hint : uint16_t;
struct Reason;
struct CompareProviders3;
template <typename T>
struct State;
struct Work;
// \brief Groups of works, these are ordered.
//
// Later items will be skipped if they are optional, or we will when backtracking,
// try a different choice for them.
enum class Group : uint8_t
{
HoldOrDelete,
NewUnsatRecommends,
// Satisfying dependencies on entirely new packages first is a good idea because
// it may contain replacement packages like libfoo1t64 whereas we later will see
// Depends: libfoo1 where libfoo1t64 Provides libfoo1 and we'd have to choose.
SatisfyNew,
Satisfy,
// On a similar note as for SatisfyNew, if the dependency contains obsolete packages
// try it last.
SatisfyObsolete,
// My intuition tells me that we should try to schedule upgrades first, then
// any non-obsolete installed packages, and only finally obsolete ones, such
// that newer packages guide resolution of dependencies for older ones, they
// may have more stringent dependencies, like a (>> 2) whereas an obsolete
// package may have a (>> 1), for example.
UpgradeManual,
InstallManual,
ObsoleteManual,
// Automatically installed packages must come last in the group, this allows
// us to see if they were installed as a dependency of a manually installed package,
// allowing a simple implementation of an autoremoval code.
UpgradeAuto,
KeepAuto,
ObsoleteAuto
};
// \brief Type to record depth at. This may very well be a 16-bit
// unsigned integer, then change Solver::State::Decision to be a
// uint16_t class enum as well to get a more compact space.
using depth_type = unsigned int;
// Documentation
template <typename T>
using heap = std::vector<T>;
static_assert(sizeof(depth_type) >= sizeof(map_id_t));
// Cache is needed to construct Iterators from Version objects we see
pkgCache &cache;
// Policy is needed for determining candidate version.
pkgDepCache::Policy &policy;
// States for packages
std::vector<State<pkgCache::Package>> pkgStates{};
// States for versions
std::vector<State<pkgCache::Version>> verStates{};
// \brief Helper function for safe access to package state.
inline State<pkgCache::Package> &operator[](pkgCache::Package *P)
{
return pkgStates[P->ID];
}
// \brief Helper function for safe access to version state.
inline State<pkgCache::Version> &operator[](pkgCache::Version *V)
{
return verStates[V->ID];
}
mutable std::vector<char> pkgObsolete;
bool Obsolete(pkgCache::PkgIterator pkg) const;
bool ObsoletedByNewerSourceVersion(pkgCache::VerIterator cand) const;
// \brief Heap of the remaining work.
//
// We are using an std::vector with std::make_heap(), std::push_heap(),
// and std::pop_heap() rather than a priority_queue because we need to
// be able to iterate over the queued work and see if a choice would
// invalidate any work.
heap<Work> work{};
// \brief Whether RescoreWork() actually needs to rescore the work.
bool needsRescore{false};
// \brief Current decision level.
//
// Each time a decision needs to be made we can push the item under
// consideration to our backlog of choices made and then later we can
// restore it easily.
std::vector<Work> choices{};
// \brief Backlog of solved work.
//
// Solved work may become invalidated when backtracking, so store it
// here to revisit it later.
std::vector<Work> solved{};
/// Various configuration options
// \brief Debug level
int debug{_config->FindI("Debug::APT::Solver")};
// \brief If set, we try to keep automatically installed packages installed.
bool KeepAuto{not _config->FindB("APT::Get::AutomaticRemove")};
// \brief If set, removals are allowed.
bool AllowRemove{_config->FindB("APT::Solver::Remove", true)};
// \brief If set, installs are allowed.
bool AllowInstall{_config->FindB("APT::Solver::Install", true)};
// \brief If set, we use strict pinning.
bool StrictPinning{_config->FindB("APT::Solver::Strict-Pinning", true)};
// \brief Enqueue dependencies shared by all versions of the package.
bool EnqueueCommonDependencies(pkgCache::PkgIterator Pkg);
// \brief Reject reverse dependencies. Must call std::make_heap() after.
bool RejectReverseDependencies(pkgCache::VerIterator Ver);
// \brief Enqueue a single or group
bool EnqueueOrGroup(pkgCache::DepIterator start, pkgCache::DepIterator end, Reason reason);
// \brief Check if a version is allowed by policy.
bool IsAllowedVersion(pkgCache::Version *V);
// \brief Return the current depth (choices.size() with casting)
depth_type depth()
{
return static_cast<depth_type>(choices.size());
}
public:
// \brief Create a new decision level.
bool Pop();
// \brief Revert to the previous decision level.
void Push(Work work);
// \brief Add work to our work queue.
void AddWork(Work &&work);
// \brief Rescore the work after a reject or a pop
void RescoreWorkIfNeeded();
// \brief Basic solver initializer. This cannot fail.
Solver(pkgCache &Cache, pkgDepCache::Policy &Policy);
// \brief Mark the package for install. This is annoying as it incurs a decision
bool Install(pkgCache::PkgIterator Pkg, Reason reason, Group group);
// \brief Install a version.
bool Install(pkgCache::VerIterator Ver, Reason reason, Group group);
// \brief Do not install this package
bool Reject(pkgCache::PkgIterator Pkg, Reason reason, Group group);
// \brief Do not install this version.
bool Reject(pkgCache::VerIterator Ver, Reason reason, Group group);
// \brief Apply the selections from the dep cache to the solver
bool FromDepCache(pkgDepCache &depcache);
// \brief Apply the solver result to the depCache
bool ToDepCache(pkgDepCache &depcache);
// \brief Solve the dependencies
bool Solve();
// Print dependency chain
std::string WhyStr(Reason reason);
};
}; // namespace APT
/**
* \brief Tagged union holding either a package, version, or nothing; representing the reason for installing something.
*
* We want to keep track of the reason why things are being installed such that
* we can have sensible debugging abilities.
*
* If the reason is empty, this means the package is automatically installed.
*/
struct APT::Solver::Reason
{
uint32_t IsVersion : 1;
uint32_t MapPtr : 31;
Reason() : IsVersion(0), MapPtr(0) {}
explicit Reason(pkgCache::PkgIterator const &Pkg) : IsVersion(0), MapPtr(Pkg.MapPointer()) {}
explicit Reason(pkgCache::VerIterator const &Ver) : IsVersion(1), MapPtr(Ver.MapPointer()) {}
// \brief Return the package, if any, otherwise 0.
map_pointer<pkgCache::Package> Pkg() const
{
return IsVersion ? 0 : map_pointer<pkgCache::Package>{(uint32_t)MapPtr};
}
// \brief Return the version, if any, otherwise 0.
map_pointer<pkgCache::Version> Ver() const
{
return IsVersion ? map_pointer<pkgCache::Version>{(uint32_t)MapPtr} : 0;
}
// \brief Return the package iterator if storing a package, or an empty one
pkgCache::PkgIterator Pkg(pkgCache &cache) const
{
return IsVersion ? pkgCache::PkgIterator() : pkgCache::PkgIterator(cache, cache.PkgP + Pkg());
}
// \brief Return the version iterator if storing a package, or an empty end.
pkgCache::VerIterator Ver(pkgCache &cache) const
{
return IsVersion ? pkgCache::VerIterator(cache, cache.VerP + Ver()) : pkgCache::VerIterator();
}
// \brief Check if there is no reason.
bool empty() const
{
return IsVersion == 0 && MapPtr == 0;
}
};
/**
* \brief A single work item
*
* A work item is a positive dependency that still needs to be resolved. Work
* is ordered, by depth, length of solutions, and optionality.
*
* The work can always be recalculated from the state by iterating over dependencies
* of all packages in there, finding solutions to them, and then adding all dependencies
* not yet resolved to the work queue.
*/
struct APT::Solver::Work
{
// \brief Reason for the work
Reason reason;
// \brief The depth at which the item has been added
depth_type depth;
// \brief The group we are in
Group group;
// \brief Possible solutions to this task, ordered in order of preference.
std::vector<pkgCache::Version *> solutions{};
// This is a union because we only need to store the choice we made when adding
// to the choice vector, and we don't need the size of valid choices in there.
union
{
// The choice we took
pkgCache::Version *choice;
// Number of valid choices
size_t size;
};
// \brief Whether this is an optional work item, they will be processed last
bool optional;
// \brief Whether this is an ugprade
bool upgrade;
// \brief This item should be removed from the queue.
bool dirty;
bool operator<(APT::Solver::Work const &b) const;
// \brief Dump the work item to std::cerr
void Dump(pkgCache &cache);
inline Work(Reason reason, depth_type depth, Group group, bool optional = false, bool upgrade = false) : reason(reason), depth(depth), group(group), size(0), optional(optional), upgrade(upgrade), dirty(false) {}
};
// \brief This essentially describes the install state in RFC2119 terms.
enum class APT::Solver::Decision : uint16_t
{
// \brief We have not made a choice about the package yet
NONE,
// \brief We need to install this package
MUST,
// \brief We cannot install this package (need conflicts with it)
MUSTNOT,
};
// \brief Hints for the solver about the item.
enum class APT::Solver::Hint : uint16_t
{
// \brief We have not made a choice about the package yet
NONE,
// \brief This package was listed as a Recommends of a must package,
SHOULD,
// \brief This package was listed as a Suggests of a must-not package
MAY,
};
/**
* \brief The solver state
*
* For each version, the solver records a decision at a certain level. It
* maintains an array mapping from version ID to state.
*/
template <typename T>
struct APT::Solver::State
{
// \brief The reason for causing this state (invalid for NONE).
//
// Rejects may have been caused by a later state. Consider we select
// between x1 and x2 in depth = N. If we now find dependencies of x1
// leading to a conflict with a package in K < N, we will record all
// of them as REJECT in depth = K.
//
// You can follow the reason chain upwards as long as the depth
// doesn't increase to unwind.
//
// Reasons < 0 are package ID, reasons > 0 are version IDs.
Reason reason{};
// \brief The depth at which the decision has been taken
depth_type depth{0};
// \brief This essentially describes the install state in RFC2119 terms.
Decision decision{Decision::NONE};
// \brief Any hint.
Hint hint{Hint::NONE};
};
|