text: /*-------------------------------------------------------------------------
   *
   * smgr.c
   *	  public interface routines to storage manager switch.
   *
   *	  All file system operations in POSTGRES dispatch through these
   *	  routines.
   *
   * Portions Copyright (c) 1996-2021, PostgreSQL Global Development Group
   * Portions Copyright (c) 1994, Regents of the University of California
   *
   *
   * IDENTIFICATION
   *	  src/backend/storage/smgr/smgr.c
   *
   *-------------------------------------------------------------------------
   */
  #include "postgres.h"
  
  #include "access/xlog.h"
  #include "lib/ilist.h"
  #include "storage/bufmgr.h"
  #include "storage/ipc.h"
  #include "storage/md.h"
  #include "storage/smgr.h"
  #include "utils/hsearch.h"
  #include "utils/inval.h"
  
  
  /*
   * This struct of function pointers defines the API between smgr.c and
   * any individual storage manager module.  Note that smgr subfunctions are
   * generally expected to report problems via elog(ERROR).  An exception is
   * that smgr_unlink should use elog(WARNING), rather than erroring out,
   * because we normally unlink relations during post-commit/abort cleanup,
   * and so it's too late to raise an error.  Also, various conditions that
   * would normally be errors should be allowed during bootstrap and/or WAL
   * recovery --- see comments in md.c for details.
   */
  typedef struct f_smgr
  {
  	void		(*smgr_init) (void);	/* may be NULL */
  	void		(*smgr_shutdown) (void);	/* may be NULL */
  	void		(*smgr_open) (SMgrRelation reln);
  	void		(*smgr_close) (SMgrRelation reln, ForkNumber forknum);
  	void		(*smgr_create) (SMgrRelation reln, ForkNumber forknum,
  								bool isRedo);
  	bool		(*smgr_exists) (SMgrRelation reln, ForkNumber forknum);
  	void		(*smgr_unlink) (RelFileNodeBackend rnode, ForkNumber forknum,
  								bool isRedo);
  	void		(*smgr_extend) (SMgrRelation reln, ForkNumber forknum,
  								BlockNumber blocknum, char *buffer, bool skipFsync);
  	bool		(*smgr_prefetch) (SMgrRelation reln, ForkNumber forknum,
  								  BlockNumber blocknum);
  	void		(*smgr_read) (SMgrRelation reln, ForkNumber forknum,
  							  BlockNumber blocknum, char *buffer);
  	void		(*smgr_write) (SMgrRelation reln, ForkNumber forknum,
  							   BlockNumber blocknum, char *buffer, bool skipFsync);
  	void		(*smgr_writeback) (SMgrRelation reln, ForkNumber forknum,
  								   BlockNumber blocknum, BlockNumber nblocks);
  	BlockNumber (*smgr_nblocks) (SMgrRelation reln, ForkNumber forknum);
  	void		(*smgr_truncate) (SMgrRelation reln, ForkNumber forknum,
  								  BlockNumber nblocks);
  	void		(*smgr_immedsync) (SMgrRelation reln, ForkNumber forknum);
  } f_smgr;
  
  static const f_smgr smgrsw[] = {
  	/* magnetic disk */
  	{
  		.smgr_init = mdinit,
  		.smgr_shutdown = NULL,
  		.smgr_open = mdopen,
  		.smgr_close = mdclose,
  		.smgr_create = mdcreate,
  		.smgr_exists = mdexists,
  		.smgr_unlink = mdunlink,
  		.smgr_extend = mdextend,
  		.smgr_prefetch = mdprefetch,
  		.smgr_read = mdread,
  		.smgr_write = mdwrite,
  		.smgr_writeback = mdwriteback,
  		.smgr_nblocks = mdnblocks,
  		.smgr_truncate = mdtruncate,
  		.smgr_immedsync = mdimmedsync,
  	}
  };
  
  static const int NSmgr = lengthof(smgrsw);
  
  /*
   * Each backend has a hashtable that stores all extant SMgrRelation objects.
   * In addition, "unowned" SMgrRelation objects are chained together in a list.
   */
  static HTAB *SMgrRelationHash = NULL;
  
  static dlist_head unowned_relns;
  
  /* local function prototypes */
  static void smgrshutdown(int code, Datum arg);
  
  
  /*
   *	smgrinit(), smgrshutdown() -- Initialize or shut down storage
   *								  managers.
   *
   * Note: smgrinit is called during backend startup (normal or standalone
   * case), *not* during postmaster start.  Therefore, any resources created
   * here or destroyed in smgrshutdown are backend-local.
   */
  void
  smgrinit(void)
  {
  	int			i;
  
  	for (i = 0; i < NSmgr; i++)
  	{
  		if (smgrsw[i].smgr_init)
  			smgrsw[i].smgr_init();
  	}
  
  	/* register the shutdown proc */
  	on_proc_exit(smgrshutdown, 0);
  }
  
  /*
   * on_proc_exit hook for smgr cleanup during backend shutdown
   */
  static void
  smgrshutdown(int code, Datum arg)
  {
  	int			i;
  
  	for (i = 0; i < NSmgr; i++)
  	{
  		if (smgrsw[i].smgr_shutdown)
  			smgrsw[i].smgr_shutdown();
  	}
  }
  
  /*
   *	smgropen() -- Return an SMgrRelation object, creating it if need be.
   *
   *		This does not attempt to actually open the underlying file.
   */
  SMgrRelation
  smgropen(RelFileNode rnode, BackendId backend)
  {
  	RelFileNodeBackend brnode;
  	SMgrRelation reln;
  	bool		found;
  
  	if (SMgrRelationHash == NULL)
  	{
  		/* First time through: initialize the hash table */
  		HASHCTL		ctl;
  
  		ctl.keysize = sizeof(RelFileNodeBackend);
  		ctl.entrysize = sizeof(SMgrRelationData);
  		SMgrRelationHash = hash_create("smgr relation table", 400,
  									   &ctl, HASH_ELEM | HASH_BLOBS);
  		dlist_init(&unowned_relns);
  	}
  
  	/* Look up or create an entry */
  	brnode.node = rnode;
  	brnode.backend = backend;
  	reln = (SMgrRelation) hash_search(SMgrRelationHash,
  									  (void *) &brnode,
  									  HASH_ENTER, &found);
  
  	/* Initialize it if not present before */
  	if (!found)
  	{
  		/* hash_search already filled in the lookup key */
  		reln->smgr_owner = NULL;
  		reln->smgr_targblock = InvalidBlockNumber;
  		for (int i = 0; i <= MAX_FORKNUM; ++i)
  			reln->smgr_cached_nblocks[i] = InvalidBlockNumber;
  		reln->smgr_which = 0;	/* we only have md.c at present */
  
  		/* implementation-specific initialization */
  		smgrsw[reln->smgr_which].smgr_open(reln);
  
  		/* it has no owner yet */
  		dlist_push_tail(&unowned_relns, &reln->node);
  	}
  
  	return reln;
  }
  
  /*
   * smgrsetowner() -- Establish a long-lived reference to an SMgrRelation object
   *
   * There can be only one owner at a time; this is sufficient since currently
   * the only such owners exist in the relcache.
   */
  void
  smgrsetowner(SMgrRelation *owner, SMgrRelation reln)
  {
  	/* We don't support "disowning" an SMgrRelation here, use smgrclearowner */
  	Assert(owner != NULL);
  
  	/*
  	 * First, unhook any old owner.  (Normally there shouldn't be any, but it
  	 * seems possible that this can happen during swap_relation_files()
  	 * depending on the order of processing.  It's ok to close the old
  	 * relcache entry early in that case.)
  	 *
  	 * If there isn't an old owner, then the reln should be in the unowned
  	 * list, and we need to remove it.
  	 */
  	if (reln->smgr_owner)
  		*(reln->smgr_owner) = NULL;
  	else
  		dlist_delete(&reln->node);
  
  	/* Now establish the ownership relationship. */
  	reln->smgr_owner = owner;
  	*owner = reln;
  }
  
  /*
   * smgrclearowner() -- Remove long-lived reference to an SMgrRelation object
   *					   if one exists
   */
  void
  smgrclearowner(SMgrRelation *owner, SMgrRelation reln)
  {
  	/* Do nothing if the SMgrRelation object is not owned by the owner */
  	if (reln->smgr_owner != owner)
  		return;
  
  	/* unset the owner's reference */
  	*owner = NULL;
  
  	/* unset our reference to the owner */
  	reln->smgr_owner = NULL;
  
  	/* add to list of unowned relations */
  	dlist_push_tail(&unowned_relns, &reln->node);
  }
  
  /*
   *	smgrexists() -- Does the underlying file for a fork exist?
   */
  bool
  smgrexists(SMgrRelation reln, ForkNumber forknum)
  {
  	return smgrsw[reln->smgr_which].smgr_exists(reln, forknum);
  }
  
  /*
   *	smgrclose() -- Close and delete an SMgrRelation object.
   */
  void
  smgrclose(SMgrRelation reln)
  {
  	SMgrRelation *owner;
  	ForkNumber	forknum;
  
  	for (forknum = 0; forknum <= MAX_FORKNUM; forknum++)
  		smgrsw[reln->smgr_which].smgr_close(reln, forknum);
  
  	owner = reln->smgr_owner;
  
  	if (!owner)
  		dlist_delete(&reln->node);
  
  	if (hash_search(SMgrRelationHash,
  					(void *) &(reln->smgr_rnode),
  					HASH_REMOVE, NULL) == NULL)
  		elog(ERROR, "SMgrRelation hashtable corrupted");
  
  	/*
  	 * Unhook the owner pointer, if any.  We do this last since in the remote
  	 * possibility of failure above, the SMgrRelation object will still exist.
  	 */
  	if (owner)
  		*owner = NULL;
  }
  
  /*
   *	smgrcloseall() -- Close all existing SMgrRelation objects.
   */
  void
  smgrcloseall(void)
  {
  	HASH_SEQ_STATUS status;
  	SMgrRelation reln;
  
  	/* Nothing to do if hashtable not set up */
  	if (SMgrRelationHash == NULL)
  		return;
  
  	hash_seq_init(&status, SMgrRelationHash);
  
  	while ((reln = (SMgrRelation) hash_seq_search(&status)) != NULL)
  		smgrclose(reln);
  }
  
  /*
   *	smgrclosenode() -- Close SMgrRelation object for given RelFileNode,
   *					   if one exists.
   *
   * This has the same effects as smgrclose(smgropen(rnode)), but it avoids
   * uselessly creating a hashtable entry only to drop it again when no
   * such entry exists already.
   */
  void
  smgrclosenode(RelFileNodeBackend rnode)
  {
  	SMgrRelation reln;
  
  	/* Nothing to do if hashtable not set up */
  	if (SMgrRelationHash == NULL)
  		return;
  
  	reln = (SMgrRelation) hash_search(SMgrRelationHash,
  									  (void *) &rnode,
  									  HASH_FIND, NULL);
  	if (reln != NULL)
  		smgrclose(reln);
  }
  
  /*
   *	smgrcreate() -- Create a new relation.
   *
   *		Given an already-created (but presumably unused) SMgrRelation,
   *		cause the underlying disk file or other storage for the fork
   *		to be created.
   */
  void
  smgrcreate(SMgrRelation reln, ForkNumber forknum, bool isRedo)
  {
  	smgrsw[reln->smgr_which].smgr_create(reln, forknum, isRedo);
  }
  
  /*
   *	smgrdosyncall() -- Immediately sync all forks of all given relations
   *
   *		All forks of all given relations are synced out to the store.
   *
   *		This is equivalent to FlushRelationBuffers() for each smgr relation,
   *		then calling smgrimmedsync() for all forks of each relation, but it's
   *		significantly quicker so should be preferred when possible.
   */
  void
  smgrdosyncall(SMgrRelation *rels, int nrels)
  {
  	int			i = 0;
  	ForkNumber	forknum;
  
  	if (nrels == 0)
  		return;
  
  	FlushRelationsAllBuffers(rels, nrels);
  
  	/*
  	 * Sync the physical file(s).
  	 */
  	for (i = 0; i < nrels; i++)
  	{
  		int			which = rels[i]->smgr_which;
  
  		for (forknum = 0; forknum <= MAX_FORKNUM; forknum++)
  		{
  			if (smgrsw[which].smgr_exists(rels[i], forknum))
  				smgrsw[which].smgr_immedsync(rels[i], forknum);
  		}
  	}
  }
  
  /*
   *	smgrdounlinkall() -- Immediately unlink all forks of all given relations
   *
   *		All forks of all given relations are removed from the store.  This
   *		should not be used during transactional operations, since it can't be
   *		undone.
   *
   *		If isRedo is true, it is okay for the underlying file(s) to be gone
   *		already.
   */
  void
  smgrdounlinkall(SMgrRelation *rels, int nrels, bool isRedo)
  {
  	int			i = 0;
  	RelFileNodeBackend *rnodes;
  	ForkNumber	forknum;
  
  	if (nrels == 0)
  		return;
  
  	/*
  	 * create an array which contains all relations to be dropped, and close
  	 * each relation's forks at the smgr level while at it
  	 */
  	rnodes = palloc(sizeof(RelFileNodeBackend) * nrels);
  	for (i = 0; i < nrels; i++)
  	{
  		RelFileNodeBackend rnode = rels[i]->smgr_rnode;
  		int			which = rels[i]->smgr_which;
  
  		rnodes[i] = rnode;
  
  		/* Close the forks at smgr level */
  		for (forknum = 0; forknum <= MAX_FORKNUM; forknum++)
  			smgrsw[which].smgr_close(rels[i], forknum);
  	}
  
  	/*
  	 * Get rid of any remaining buffers for the relations.  bufmgr will just
  	 * drop them without bothering to write the contents.
  	 */
  	DropRelFileNodesAllBuffers(rnodes, nrels);
  
  	/*
  	 * It'd be nice to tell the stats collector to forget them immediately,
  	 * too. But we can't because we don't know the OIDs.
  	 */
  
  	/*
  	 * Send a shared-inval message to force other backends to close any
  	 * dangling smgr references they may have for these rels.  We should do
  	 * this before starting the actual unlinking, in case we fail partway
  	 * through that step.  Note that the sinval messages will eventually come
  	 * back to this backend, too, and thereby provide a backstop that we
  	 * closed our own smgr rel.
  	 */
  	for (i = 0; i < nrels; i++)
  		CacheInvalidateSmgr(rnodes[i]);
  
  	/*
  	 * Delete the physical file(s).
  	 *
  	 * Note: smgr_unlink must treat deletion failure as a WARNING, not an
  	 * ERROR, because we've already decided to commit or abort the current
  	 * xact.
  	 */
  
  	for (i = 0; i < nrels; i++)
  	{
  		int			which = rels[i]->smgr_which;
  
  		for (forknum = 0; forknum <= MAX_FORKNUM; forknum++)
  			smgrsw[which].smgr_unlink(rnodes[i], forknum, isRedo);
  	}
  
  	pfree(rnodes);
  }
  
  
  /*
   *	smgrextend() -- Add a new block to a file.
   *
   *		The semantics are nearly the same as smgrwrite(): write at the
   *		specified position.  However, this is to be used for the case of
   *		extending a relation (i.e., blocknum is at or beyond the current
   *		EOF).  Note that we assume writing a block beyond current EOF
   *		causes intervening file space to become filled with zeroes.
   */
  void
  smgrextend(SMgrRelation reln, ForkNumber forknum, BlockNumber blocknum,
  		   char *buffer, bool skipFsync)
  {
  	smgrsw[reln->smgr_which].smgr_extend(reln, forknum, blocknum,
  										 buffer, skipFsync);
  
  	/*
  	 * Normally we expect this to increase nblocks by one, but if the cached
  	 * value isn't as expected, just invalidate it so the next call asks the
  	 * kernel.
  	 */
  	if (reln->smgr_cached_nblocks[forknum] == blocknum)
  		reln->smgr_cached_nblocks[forknum] = blocknum + 1;
  	else
  		reln->smgr_cached_nblocks[forknum] = InvalidBlockNumber;
  }
  
  /*
   *	smgrprefetch() -- Initiate asynchronous read of the specified block of a relation.
   *
   *		In recovery only, this can return false to indicate that a file
   *		doesn't	exist (presumably it has been dropped by a later WAL
   *		record).
   */
  bool
  smgrprefetch(SMgrRelation reln, ForkNumber forknum, BlockNumber blocknum)
  {
  	return smgrsw[reln->smgr_which].smgr_prefetch(reln, forknum, blocknum);
  }
  
  /*
   *	smgrread() -- read a particular block from a relation into the supplied
   *				  buffer.
   *
   *		This routine is called from the buffer manager in order to
   *		instantiate pages in the shared buffer cache.  All storage managers
   *		return pages in the format that POSTGRES expects.
   */
  void
  smgrread(SMgrRelation reln, ForkNumber forknum, BlockNumber blocknum,
  		 char *buffer)
  {
  	smgrsw[reln->smgr_which].smgr_read(reln, forknum, blocknum, buffer);
  }
  
  /*
   *	smgrwrite() -- Write the supplied buffer out.
   *
   *		This is to be used only for updating already-existing blocks of a
   *		relation (ie, those before the current EOF).  To extend a relation,
   *		use smgrextend().
   *
   *		This is not a synchronous write -- the block is not necessarily
   *		on disk at return, only dumped out to the kernel.  However,
   *		provisions will be made to fsync the write before the next checkpoint.
   *
   *		skipFsync indicates that the caller will make other provisions to
   *		fsync the relation, so we needn't bother.  Temporary relations also
   *		do not require fsync.
   */
  void
  smgrwrite(SMgrRelation reln, ForkNumber forknum, BlockNumber blocknum,
  		  char *buffer, bool skipFsync)
  {
  	smgrsw[reln->smgr_which].smgr_write(reln, forknum, blocknum,
  										buffer, skipFsync);
  }
  
  
  /*
   *	smgrwriteback() -- Trigger kernel writeback for the supplied range of
   *					   blocks.
   */
  void
  smgrwriteback(SMgrRelation reln, ForkNumber forknum, BlockNumber blocknum,
  			  BlockNumber nblocks)
  {
  	smgrsw[reln->smgr_which].smgr_writeback(reln, forknum, blocknum,
  											nblocks);
  }
  
  /*
   *	smgrnblocks() -- Calculate the number of blocks in the
   *					 supplied relation.
   */
  BlockNumber
  smgrnblocks(SMgrRelation reln, ForkNumber forknum)
  {
  	BlockNumber result;
  
  	/*
  	 * For now, we only use cached values in recovery due to lack of a shared
  	 * invalidation mechanism for changes in file size.
  	 */
  	if (InRecovery && reln->smgr_cached_nblocks[forknum] != InvalidBlockNumber)
  		return reln->smgr_cached_nblocks[forknum];
  
  	result = smgrsw[reln->smgr_which].smgr_nblocks(reln, forknum);
  
  	reln->smgr_cached_nblocks[forknum] = result;
  
  	return result;
  }
  
  /*
   *	smgrtruncate() -- Truncate the given forks of supplied relation to
   *					  each specified numbers of blocks
   *
   * The truncation is done immediately, so this can't be rolled back.
   *
   * The caller must hold AccessExclusiveLock on the relation, to ensure that
   * other backends receive the smgr invalidation event that this function sends
   * before they access any forks of the relation again.
   */
  void
  smgrtruncate(SMgrRelation reln, ForkNumber *forknum, int nforks, BlockNumber *nblocks)
  {
  	int			i;
  
  	/*
  	 * Get rid of any buffers for the about-to-be-deleted blocks. bufmgr will
  	 * just drop them without bothering to write the contents.
  	 */
  	DropRelFileNodeBuffers(reln->smgr_rnode, forknum, nforks, nblocks);
  
  	/*
  	 * Send a shared-inval message to force other backends to close any smgr
  	 * references they may have for this rel.  This is useful because they
  	 * might have open file pointers to segments that got removed, and/or
  	 * smgr_targblock variables pointing past the new rel end.  (The inval
  	 * message will come back to our backend, too, causing a
  	 * probably-unnecessary local smgr flush.  But we don't expect that this
  	 * is a performance-critical path.)  As in the unlink code, we want to be
  	 * sure the message is sent before we start changing things on-disk.
  	 */
  	CacheInvalidateSmgr(reln->smgr_rnode);
  
  	/* Do the truncation */
  	for (i = 0; i < nforks; i++)
  	{
  		/* Make the cached size is invalid if we encounter an error. */
  		reln->smgr_cached_nblocks[forknum[i]] = InvalidBlockNumber;
  
  		smgrsw[reln->smgr_which].smgr_truncate(reln, forknum[i], nblocks[i]);
  
  		/*
  		 * We might as well update the local smgr_cached_nblocks values. The
  		 * smgr cache inval message that this function sent will cause other
  		 * backends to invalidate their copies of smgr_fsm_nblocks and
  		 * smgr_vm_nblocks, and these ones too at the next command boundary.
  		 * But these ensure they aren't outright wrong until then.
  		 */
  		reln->smgr_cached_nblocks[forknum[i]] = nblocks[i];
  	}
  }
  
  /*
   *	smgrimmedsync() -- Force the specified relation to stable storage.
   *
   *		Synchronously force all previous writes to the specified relation
   *		down to disk.
   *
   *		This is useful for building completely new relations (eg, new
   *		indexes).  Instead of incrementally WAL-logging the index build
   *		steps, we can just write completed index pages to disk with smgrwrite
   *		or smgrextend, and then fsync the completed index file before
   *		committing the transaction.  (This is sufficient for purposes of
   *		crash recovery, since it effectively duplicates forcing a checkpoint
   *		for the completed index.  But it is *not* sufficient if one wishes
   *		to use the WAL log for PITR or replication purposes: in that case
   *		we have to make WAL entries as well.)
   *
   *		The preceding writes should specify skipFsync = true to avoid
   *		duplicative fsyncs.
   *
   *		Note that you need to do FlushRelationBuffers() first if there is
   *		any possibility that there are dirty buffers for the relation;
   *		otherwise the sync is not very meaningful.
   */
  void
  smgrimmedsync(SMgrRelation reln, ForkNumber forknum)
  {
  	smgrsw[reln->smgr_which].smgr_immedsync(reln, forknum);
  }
  
  /*
   * AtEOXact_SMgr
   *
   * This routine is called during transaction commit or abort (it doesn't
   * particularly care which).  All transient SMgrRelation objects are closed.
   *
   * We do this as a compromise between wanting transient SMgrRelations to
   * live awhile (to amortize the costs of blind writes of multiple blocks)
   * and needing them to not live forever (since we're probably holding open
   * a kernel file descriptor for the underlying file, and we need to ensure
   * that gets closed reasonably soon if the file gets deleted).
   */
  void
  AtEOXact_SMgr(void)
  {
  	dlist_mutable_iter iter;
  
  	/*
  	 * Zap all unowned SMgrRelations.  We rely on smgrclose() to remove each
  	 * one from the list.
  	 */
  	dlist_foreach_modify(iter, &unowned_relns)
  	{
  		SMgrRelation rel = dlist_container(SMgrRelationData, node,
  										   iter.cur);
  
  		Assert(rel->smgr_owner == NULL);
  
  		smgrclose(rel);
  	}
  }
  