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I tried to preserve most errno values, but in some cases they were
inconsistent (different errno values for the same error name) or just
mismatched.
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This is a rewrite of the hashmap implementation. Its advantage is lower
memory usage.
It uses open addressing (entries are stored in an array, as opposed to
linked lists). Hash collisions are resolved with linear probing and
Robin Hood displacement policy. See the references in hashmap.c.
Some fun empirical findings about hashmap usage in systemd on my laptop:
- 98 % of allocated hashmaps are Sets.
- Sets contain 78 % of all entries, plain Hashmaps 17 %, and
OrderedHashmaps 5 %.
- 60 % of allocated hashmaps contain only 1 entry.
- 90 % of allocated hashmaps contain 5 or fewer entries.
- 75 % of all entries are in hashmaps that use trivial_hash_ops.
Clearly it makes sense to:
- store entries in distinct entry types. Especially for Sets - their
entries are the most numerous and they require the least information
to store an entry.
- have a way to store small numbers of entries directly in the hashmap
structs, and only allocate the usual entry arrays when the direct
storage is full.
The implementation has an optional debugging feature (enabled by
defining the ENABLE_HASHMAP_DEBUG macro), where it:
- tracks all allocated hashmaps in a linked list so that one can
easily find them in gdb,
- tracks which function/line allocated a given hashmap, and
- checks for invalid mixing of hashmap iteration and modification.
Since entries are not allocated one-by-one anymore, mempools are not
used for entries. Originally I meant to drop mempools entirely, but it's
still worth it to use them for the hashmap structs. My testing indicates
that it makes loading of units about 5 % faster (a test with 10000 units
where more than 200000 hashmaps are allocated - pure malloc: 449±4 ms,
mempools: 427±7 ms).
Here are some memory usage numbers, taken on my laptop with a more or
less normal Fedora setup after booting with SELinux disabled (SELinux
increases systemd's memory usage significantly):
systemd (PID 1) Original New Change
dirty memory (from pmap -x 1) [KiB] 2152 1264 -41 %
total heap allocations (from gdb-heap) [KiB] 1623 756 -53 %
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Add mempool_alloc0_tile(). It's like mempool_alloc_tile(), but it
initializes the allocated tile's memory to zero.
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Two's logarithms for unsigned.
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provided headers
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We really shouldn't create fds ever that have the flag unset.
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278 is vmsplice on x86_64. 318 is what we want:
http://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git/tree/arch/x86/syscalls/syscall_64.tbl
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needing entropy
Doesn't require an fd, and could be a bit faster, so let's make use of
it, if it is available.
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something fails
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These use the (deprecated) IPv4 address classes to deduce the corresponding subnet masks. This is useful when addresses
without subnet masks and prefix lengths are given.
Make use of these new functions from sd-dhcp-lease.
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Reported-by: sztanpet on irc
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Function queries system hostname and applies changes only when necessary. Also,
migrate all client of sethostname to sethostname_idempotent while at it.
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On an ro fs, systemctl disable ... would fail silently.
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https://bugs.freedesktop.org/show_bug.cgi?id=85447
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Let's make parse_usec() and parse_nsec() work similar
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In order to make object destruction easier (in particular in combination
with _cleanup_) we usually make destructors deal with NULL objects as
NOPs. Change the calendar spec destructor to follow the same scheme.
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Normally we shouldn#t log from "library" functions, but SELinux is
weird, hence upgrade security messages uniformly to LOG_ERR when in
enforcing mode.
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APIs that query and return something cannot silently fail, they must
either return something useful, or an error. Fix that.
Also, properly rollback socket unit fd creation when something goes
wrong with the security framework.
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of the matching selinux code
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previously mac_smack_apply(path, NULL) would operate on the symlink
itself while mac_smack_apply(path, "foo") would follow the symlink.
Let's clean this up an always operate on the symlink, which appears to
be the safer option.
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a) always return negative errno error codes
b) always become a noop if smack is off
c) always take a NULL label as a request to remove it
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and all that reset it to defaults mac_{selinux|smack}_fix()
Let's clean up the naming schemes a bit and use the same one for SMACK
and for SELINUX.
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It cannot fail in the current hashmap implementation, but it may fail in
alternative implementations (unless a sufficiently large reservation has
been placed beforehand).
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That hashmap_move_one() currently cannot fail with -ENOMEM is an
implementation detail, which is not possible to guarantee in general.
Hashmap implementations based on anything else than chaining of
individual entries may have to allocate.
hashmap_move_one will not fail with -ENOMEM if a proper reservation has
been made beforehand. Use reservations in install.c.
In cgtop.c simply propagate the error instead of asserting.
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With the current hashmap implementation that uses chaining, placing a
reservation can serve two purposes:
- To optimize putting of entries if the number of entries to put is
known. The reservation allocates buckets, so later resizing can be
avoided.
- To avoid having very long bucket chains after using
hashmap_move(_one).
In an alternative hashmap implementation it will serve an additional
purpose:
- To guarantee a subsequent hashmap_move(_one) will not fail with
-ENOMEM (this never happens in the current implementation).
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Return 0 if no resize was needed, 1 if successfully resized and
negative on error.
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It appears order may matter here. Use OrderedHashmaps to be safe.
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It's handled just fine by returning NULL.
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-ENOENT is the same return value as if 'other' were an allocated hashmap
that does not contain the key. A NULL hashmap is a possible way of
expressing a hashmap that contains no key.
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