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37c87e63f9
For AIO, and also some other recent patches, we need the ability to call relpath() in a critical section. Until now that was not feasible, as it allocated memory. The fact that relpath() allocated memory also made it awkward to use in log messages because we had to take care to free the memory afterwards. Which we e.g. didn't do for when zeroing out an invalid buffer. We discussed other solutions, e.g. filling a pre-allocated buffer that's passed to relpath(), but they all came with plenty downsides or were larger projects. The easiest fix seems to be to make relpath() return the path by value. To be able to return the path by value we need to determine the maximum length of a relation path. This patch adds a long #define that computes the exact maximum, which is verified to be correct in a regression test. As this change the signature of relpath(), extensions using it will need to adapt their code. We discussed leaving a backward-compat shim in place, but decided it's not worth it given the use of relpath() doesn't seem widespread. Discussion: https://postgr.es/m/xeri5mla4b5syjd5a25nok5iez2kr3bm26j2qn4u7okzof2bmf@kwdh2vf7npra
155 lines
4.5 KiB
C
155 lines
4.5 KiB
C
/*-------------------------------------------------------------------------
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*
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* relpath.h
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* Declarations for GetRelationPath() and friends
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*
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* Portions Copyright (c) 1996-2025, PostgreSQL Global Development Group
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* Portions Copyright (c) 1994, Regents of the University of California
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*
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* src/include/common/relpath.h
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*
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*-------------------------------------------------------------------------
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*/
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#ifndef RELPATH_H
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#define RELPATH_H
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/*
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* Required here; note that CppAsString2() does not throw an error if the
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* symbol is not defined.
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*/
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#include "catalog/catversion.h"
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/*
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* RelFileNumber data type identifies the specific relation file name.
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*/
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typedef Oid RelFileNumber;
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#define InvalidRelFileNumber ((RelFileNumber) InvalidOid)
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#define RelFileNumberIsValid(relnumber) \
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((bool) ((relnumber) != InvalidRelFileNumber))
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/*
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* Name of major-version-specific tablespace subdirectories
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*/
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#define TABLESPACE_VERSION_DIRECTORY "PG_" PG_MAJORVERSION "_" \
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CppAsString2(CATALOG_VERSION_NO)
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/*
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* Tablespace path (relative to installation's $PGDATA).
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*
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* These values should not be changed as many tools rely on it.
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*/
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#define PG_TBLSPC_DIR "pg_tblspc"
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#define PG_TBLSPC_DIR_SLASH "pg_tblspc/" /* required for strings
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* comparisons */
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/* Characters to allow for an OID in a relation path */
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#define OIDCHARS 10 /* max chars printed by %u */
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/*
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* Stuff for fork names.
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*
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* The physical storage of a relation consists of one or more forks.
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* The main fork is always created, but in addition to that there can be
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* additional forks for storing various metadata. ForkNumber is used when
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* we need to refer to a specific fork in a relation.
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*/
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typedef enum ForkNumber
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{
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InvalidForkNumber = -1,
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MAIN_FORKNUM = 0,
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FSM_FORKNUM,
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VISIBILITYMAP_FORKNUM,
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INIT_FORKNUM,
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/*
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* NOTE: if you add a new fork, change MAX_FORKNUM and possibly
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* FORKNAMECHARS below, and update the forkNames array in
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* src/common/relpath.c
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*/
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} ForkNumber;
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#define MAX_FORKNUM INIT_FORKNUM
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#define FORKNAMECHARS 4 /* max chars for a fork name */
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extern PGDLLIMPORT const char *const forkNames[];
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extern ForkNumber forkname_to_number(const char *forkName);
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extern int forkname_chars(const char *str, ForkNumber *fork);
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/*
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* Unfortunately, there's no easy way to derive PROCNUMBER_CHARS from
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* MAX_BACKENDS. MAX_BACKENDS is 2^18-1. Crosschecked in test_relpath().
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*/
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#define PROCNUMBER_CHARS 6
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/*
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* The longest possible relation path lengths is from the following format:
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* sprintf(rp.path, "%s/%u/%s/%u/t%d_%u",
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* PG_TBLSPC_DIR, spcOid,
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* TABLESPACE_VERSION_DIRECTORY,
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* dbOid, procNumber, relNumber);
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*
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* Note this does *not* include the trailing null-byte, to make it easier to
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* combine it with other lengths.
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*/
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#define REL_PATH_STR_MAXLEN \
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( \
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sizeof(PG_TBLSPC_DIR) - 1 \
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+ sizeof((char)'/') \
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+ OIDCHARS /* spcOid */ \
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+ sizeof((char)'/') \
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+ sizeof(TABLESPACE_VERSION_DIRECTORY) - 1 \
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+ sizeof((char)'/') \
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+ OIDCHARS /* dbOid */ \
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+ sizeof((char)'/') \
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+ sizeof((char)'t') /* temporary table indicator */ \
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+ PROCNUMBER_CHARS /* procNumber */ \
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+ sizeof((char)'_') \
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+ OIDCHARS /* relNumber */ \
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+ sizeof((char)'_') \
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+ FORKNAMECHARS /* forkNames[forkNumber] */ \
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)
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/*
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* String of the exact length required to represent a relation path. We return
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* this struct, instead of char[REL_PATH_STR_MAXLEN + 1], as the pointer would
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* decay to a plain char * too easily, possibly preventing the compiler from
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* detecting invalid references to the on-stack return value of
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* GetRelationPath().
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*/
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typedef struct RelPathStr
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{
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char str[REL_PATH_STR_MAXLEN + 1];
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} RelPathStr;
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/*
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* Stuff for computing filesystem pathnames for relations.
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*/
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extern char *GetDatabasePath(Oid dbOid, Oid spcOid);
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extern RelPathStr GetRelationPath(Oid dbOid, Oid spcOid, RelFileNumber relNumber,
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int procNumber, ForkNumber forkNumber);
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/*
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* Wrapper macros for GetRelationPath. Beware of multiple
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* evaluation of the RelFileLocator or RelFileLocatorBackend argument!
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*/
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/* First argument is a RelFileLocator */
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#define relpathbackend(rlocator, backend, forknum) \
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GetRelationPath((rlocator).dbOid, (rlocator).spcOid, (rlocator).relNumber, \
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backend, forknum)
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/* First argument is a RelFileLocator */
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#define relpathperm(rlocator, forknum) \
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relpathbackend(rlocator, INVALID_PROC_NUMBER, forknum)
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/* First argument is a RelFileLocatorBackend */
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#define relpath(rlocator, forknum) \
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relpathbackend((rlocator).locator, (rlocator).backend, forknum)
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#endif /* RELPATH_H */
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