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db_include/storage/smgr.h

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+/*-------------------------------------------------------------------------
+ *
+ * smgr.h
+ *	  storage manager switch public interface declarations.
+ *
+ *
+ * Portions Copyright (c) 1996-2021, PostgreSQL Global Development Group
+ * Portions Copyright (c) 1994, Regents of the University of California
+ *
+ * src/include/storage/smgr.h
+ *
+ *-------------------------------------------------------------------------
+ */
+#ifndef SMGR_H
+#define SMGR_H
+
+#include "lib/ilist.h"
+#include "storage/block.h"
+#include "storage/relfilenode.h"
+
+/*
+ * smgr.c maintains a table of SMgrRelation objects, which are essentially
+ * cached file handles.  An SMgrRelation is created (if not already present)
+ * by smgropen(), and destroyed by smgrclose().  Note that neither of these
+ * operations imply I/O, they just create or destroy a hashtable entry.
+ * (But smgrclose() may release associated resources, such as OS-level file
+ * descriptors.)
+ *
+ * An SMgrRelation may have an "owner", which is just a pointer to it from
+ * somewhere else; smgr.c will clear this pointer if the SMgrRelation is
+ * closed.  We use this to avoid dangling pointers from relcache to smgr
+ * without having to make the smgr explicitly aware of relcache.  There
+ * can't be more than one "owner" pointer per SMgrRelation, but that's
+ * all we need.
+ *
+ * SMgrRelations that do not have an "owner" are considered to be transient,
+ * and are deleted at end of transaction.
+ */
+typedef struct SMgrRelationData
+{
+	/* rnode is the hashtable lookup key, so it must be first! */
+	RelFileNodeBackend smgr_rnode;	/* relation physical identifier */
+
+	/* pointer to owning pointer, or NULL if none */
+	struct SMgrRelationData **smgr_owner;
+
+	/*
+	 * The following fields are reset to InvalidBlockNumber upon a cache flush
+	 * event, and hold the last known size for each fork.  This information is
+	 * currently only reliable during recovery, since there is no cache
+	 * invalidation for fork extension.
+	 */
+	BlockNumber smgr_targblock; /* current insertion target block */
+	BlockNumber smgr_cached_nblocks[MAX_FORKNUM + 1];	/* last known size */
+
+	/* additional public fields may someday exist here */
+
+	/*
+	 * Fields below here are intended to be private to smgr.c and its
+	 * submodules.  Do not touch them from elsewhere.
+	 */
+	int			smgr_which;		/* storage manager selector */
+
+	/*
+	 * for md.c; per-fork arrays of the number of open segments
+	 * (md_num_open_segs) and the segments themselves (md_seg_fds).
+	 */
+	int			md_num_open_segs[MAX_FORKNUM + 1];
+	struct _MdfdVec *md_seg_fds[MAX_FORKNUM + 1];
+
+	/* if unowned, list link in list of all unowned SMgrRelations */
+	dlist_node	node;
+} SMgrRelationData;
+
+typedef SMgrRelationData *SMgrRelation;
+
+#define SmgrIsTemp(smgr) \
+	RelFileNodeBackendIsTemp((smgr)->smgr_rnode)
+
+extern void smgrinit(void);
+extern SMgrRelation smgropen(RelFileNode rnode, BackendId backend);
+extern bool smgrexists(SMgrRelation reln, ForkNumber forknum);
+extern void smgrsetowner(SMgrRelation *owner, SMgrRelation reln);
+extern void smgrclearowner(SMgrRelation *owner, SMgrRelation reln);
+extern void smgrclose(SMgrRelation reln);
+extern void smgrcloseall(void);
+extern void smgrclosenode(RelFileNodeBackend rnode);
+extern void smgrcreate(SMgrRelation reln, ForkNumber forknum, bool isRedo);
+extern void smgrdosyncall(SMgrRelation *rels, int nrels);
+extern void smgrdounlinkall(SMgrRelation *rels, int nrels, bool isRedo);
+extern void smgrextend(SMgrRelation reln, ForkNumber forknum,
+					   BlockNumber blocknum, char *buffer, bool skipFsync);
+extern bool smgrprefetch(SMgrRelation reln, ForkNumber forknum,
+						 BlockNumber blocknum);
+extern void smgrread(SMgrRelation reln, ForkNumber forknum,
+					 BlockNumber blocknum, char *buffer);
+extern void smgrwrite(SMgrRelation reln, ForkNumber forknum,
+					  BlockNumber blocknum, char *buffer, bool skipFsync);
+extern void smgrwriteback(SMgrRelation reln, ForkNumber forknum,
+						  BlockNumber blocknum, BlockNumber nblocks);
+extern BlockNumber smgrnblocks(SMgrRelation reln, ForkNumber forknum);
+extern BlockNumber smgrnblocks_cached(SMgrRelation reln, ForkNumber forknum);
+extern void smgrtruncate(SMgrRelation reln, ForkNumber *forknum,
+						 int nforks, BlockNumber *nblocks);
+extern void smgrimmedsync(SMgrRelation reln, ForkNumber forknum);
+extern void AtEOXact_SMgr(void);
+
+#endif							/* SMGR_H */