mirror of https://github.com/schoebel/mars
107 lines
3.4 KiB
C
107 lines
3.4 KiB
C
/*
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* MARS Long Distance Replication Software
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*
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* Copyright (C) 2010-2014 Thomas Schoebel-Theuer
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* Copyright (C) 2011-2014 1&1 Internet AG
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*
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* This program is free software; you can redistribute it and/or modify
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* it under the terms of the GNU General Public License as published by
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* the Free Software Foundation; either version 2 of the License, or
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* (at your option) any later version.
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*
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* This program is distributed in the hope that it will be useful,
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* but WITHOUT ANY WARRANTY; without even the implied warranty of
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* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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* GNU General Public License for more details.
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*/
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#ifndef META_H
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#define META_H
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/***********************************************************************/
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/* metadata descriptions */
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/* The idea is to describe your C structures in such a way that
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* transfers to disk or over a network become self-describing.
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*
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* In essence, this is a kind of version-independent marshalling.
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*
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* Advantage:
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* When you extend your original C struct (and of course update the
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* corresponding meta structure), old data on disk (or network peers
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* running an old version of your program) will remain valid.
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* Upon read, newly added fields missing in the old version will be simply
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* not filled in and therefore remain zeroed (if you don't forget to
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* initially clear your structures via memset() / initializers / etc).
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* Note that this works only if you never rename or remove existing
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* fields; you should only add new ones.
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* [TODO: add macros for description of ignored / renamed fields to
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* overcome this limitation]
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* You may increase the size of integers, for example from 32bit to 64bit
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* or even higher; sign extension will be automatically carried out
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* when necessary.
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* Also, you may change the order of fields, because the metadata interpreter
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* will check each field individually; field offsets are automatically
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* maintained.
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*
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* Disadvantage: this adds some (small) overhead.
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*/
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enum field_type {
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FIELD_DONE,
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FIELD_REF,
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FIELD_SUB,
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FIELD_STRING,
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FIELD_RAW,
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FIELD_INT,
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FIELD_UINT,
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};
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struct meta {
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/* char field_name[MAX_FIELD_LEN]; */
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char *field_name;
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short field_type;
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short field_data_size;
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short field_transfer_size;
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int field_offset;
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const struct meta *field_ref;
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};
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#define _META_INI(NAME, STRUCT, TYPE, TSIZE) \
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.field_name = #NAME, \
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.field_type = TYPE, \
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.field_data_size = sizeof(((STRUCT *)NULL)->NAME), \
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.field_transfer_size = (TSIZE), \
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.field_offset = offsetof(STRUCT, NAME) \
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#define META_INI_TRANSFER(NAME, STRUCT, TYPE, TSIZE) \
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{ _META_INI(NAME, STRUCT, TYPE, TSIZE) }
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#define META_INI(NAME, STRUCT, TYPE) \
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{ _META_INI(NAME, STRUCT, TYPE, 0) }
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#define _META_INI_AIO(NAME, STRUCT, AIO) \
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.field_name = #NAME, \
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.field_type = FIELD_REF, \
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.field_data_size = sizeof(*(((STRUCT *)NULL)->NAME)), \
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.field_offset = offsetof(STRUCT, NAME), \
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.field_ref = AIO
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#define META_INI_AIO(NAME, STRUCT, AIO) { _META_INI_AIO(NAME, STRUCT, AIO) }
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#define _META_INI_SUB(NAME, STRUCT, SUB) \
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.field_name = #NAME, \
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.field_type = FIELD_SUB, \
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.field_data_size = sizeof(((STRUCT *)NULL)->NAME), \
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.field_offset = offsetof(STRUCT, NAME), \
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.field_ref = SUB
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#define META_INI_SUB(NAME, STRUCT, SUB) { _META_INI_SUB(NAME, STRUCT, SUB) }
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extern const struct meta *find_meta(const struct meta *meta, const char *field_name);
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/* extern void free_meta(void *data, const struct meta *meta); */
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#endif
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