/*-------------------------------------------------------------------------
 *
 * fd.c--
 *	  Virtual file descriptor code.
 *
 * Copyright (c) 1994, Regents of the University of California
 *
 * IDENTIFICATION
 *	  $Id: fd.c,v 1.27 1997/11/07 06:38:15 thomas Exp $
 *
 * NOTES:
 *
 * This code manages a cache of 'virtual' file descriptors (VFDs).
 * The server opens many file descriptors for a variety of reasons,
 * including base tables, scratch files (e.g., sort and hash spool
 * files), and random calls to C library routines like system(3); it
 * is quite easy to exceed system limits on the number of open files a
 * single process can have.  (This is around 256 on many modern
 * operating systems, but can be as low as 32 on others.)
 *
 * VFDs are managed as an LRU pool, with actual OS file descriptors
 * being opened and closed as needed.  Obviously, if a routine is
 * opened using these interfaces, all subsequent operations must also
 * be through these interfaces (the File type is not a real file
 * descriptor).
 *
 * For this scheme to work, most (if not all) routines throughout the
 * server should use these interfaces instead of calling the C library
 * routines (e.g., open(2) and fopen(3)) themselves.  Otherwise, we
 * may find ourselves short of real file descriptors anyway.
 *
 * This file used to contain a bunch of stuff to support RAID levels 0
 * (jbod), 1 (duplex) and 5 (xor parity).  That stuff is all gone
 * because the parallel query processing code that called it is all
 * gone.  If you really need it you could get it from the original
 * POSTGRES source.
 *-------------------------------------------------------------------------
 */

#include <sys/types.h>
#include <stdio.h>
#include <sys/file.h>
#include <sys/param.h>
#include <errno.h>
#include <sys/stat.h>
#include <string.h>
#include <unistd.h>
#include <fcntl.h>

#include "postgres.h"
#include "miscadmin.h"			/* for DataDir */
#include "utils/palloc.h"
#include "storage/fd.h"

/*
 * Problem: Postgres does a system(ld...) to do dynamic loading.  This
 * will open several extra files in addition to those used by
 * Postgres.  We need to do this hack to guarentee that there are file
 * descriptors free for ld to use.
 *
 * The current solution is to limit the number of files descriptors
 * that this code will allocated at one time.  (it leaves
 * RESERVE_FOR_LD free).
 *
 * (Even though most dynamic loaders now use dlopen(3) or the
 * equivalent, the OS must still open several files to perform the
 * dynamic loading.  Keep this here.)
 */
#ifndef RESERVE_FOR_LD
#define RESERVE_FOR_LD	10
#endif

/*
 * We need to ensure that we have at least some file descriptors
 * available to postgreSQL after we've reserved the ones for LD,
 * so we set that value here.
 *
 * I think 10 is an apropriate value so that's what it'll be
 * for now.
 */
#ifndef FD_MINFREE
#define FD_MINFREE 10
#endif

/* Debugging.... */

#ifdef FDDEBUG
#define DO_DB(A) A
#else
#define DO_DB(A)				/* A */
#endif

#define VFD_CLOSED -1

#include "storage/fd.h"
#include "utils/elog.h"

#define FileIsNotOpen(file) (VfdCache[file].fd == VFD_CLOSED)

typedef struct vfd
{
	signed short fd;
	unsigned short fdstate;

#define FD_DIRTY		(1 << 0)

	File		nextFree;
	File		lruMoreRecently;
	File		lruLessRecently;
	long		seekPos;
	char	   *fileName;
	int			fileFlags;
	int			fileMode;
} Vfd;

/*
 * Virtual File Descriptor array pointer and size.	This grows as
 * needed.
 */
static Vfd *VfdCache;
static Size SizeVfdCache = 0;

/*
 * Number of file descriptors known to be open.
 */
static int	nfile = 0;

/*
 * Private Routines
 *
 * Delete		   - delete a file from the Lru ring
 * LruDelete	   - remove a file from the Lru ring and close
 * Insert		   - put a file at the front of the Lru ring
 * LruInsert	   - put a file at the front of the Lru ring and open
 * AssertLruRoom   - make sure that there is a free fd.
 *
 * the Last Recently Used ring is a doubly linked list that begins and
 * ends on element zero.  Element zero is special -- it doesn't represent
 * a file and its "fd" field always == VFD_CLOSED.	Element zero is just an
 * anchor that shows us the beginning/end of the ring.
 *
 * example:
 *
 *	   /--less----\				   /---------\
 *	   v		   \			  v			  \
 *	 #0 --more---> LeastRecentlyUsed --more-\ \
 *	  ^\									| |
 *	   \\less--> MostRecentlyUsedFile	<---/ |
 *		\more---/					 \--less--/
 *
 * AllocateVfd	   - grab a free (or new) file record (from VfdArray)
 * FreeVfd		   - free a file record
 *
 */
static void Delete(File file);
static void LruDelete(File file);
static void Insert(File file);
static int	LruInsert(File file);
static void AssertLruRoom(void);
static File AllocateVfd(void);
static void FreeVfd(File file);

static int	FileAccess(File file);
static File fileNameOpenFile(FileName fileName, int fileFlags, int fileMode);
static char *filepath(char *filename);
static long pg_nofile(void);

int
pg_fsync(int fd)
{
	extern int	fsyncOff;

	return fsyncOff ? 0 : fsync(fd);
}

#define fsync pg_fsync

long
pg_nofile(void)
{
	static long no_files = 0;

	if (no_files == 0)
	{
#ifndef HAVE_SYSCONF
		no_files = (long) NOFILE;
#else
		no_files = sysconf(_SC_OPEN_MAX);
		if (no_files == -1)
		{
			elog(DEBUG, "pg_nofile: Unable to get _SC_OPEN_MAX using sysconf() using (%d)", NOFILE);
			no_files = (long) NOFILE;
		}
#endif
	}

	if ((no_files - RESERVE_FOR_LD) < FD_MINFREE)
		elog(FATAL, "pg_nofile: insufficient File Descriptors in postmaster to start backend (%ld).\n"
			 "                   O/S allows %ld, Postmaster reserves %d, We need %d (MIN) after that.",
		no_files - RESERVE_FOR_LD, no_files, RESERVE_FOR_LD, FD_MINFREE);
	return no_files - RESERVE_FOR_LD;
}

#if defined(FDDEBUG)
static void
_dump_lru()
{
	int			mru = VfdCache[0].lruLessRecently;
	Vfd		   *vfdP = &VfdCache[mru];
	char		buf[2048];

	sprintf(buf, "LRU: MOST %d ", mru);
	while (mru != 0)
	{
		mru = vfdP->lruLessRecently;
		vfdP = &VfdCache[mru];
		sprintf(buf + strlen(buf), "%d ", mru);
	}
	sprintf(buf + strlen(buf), "LEAST");
	elog(DEBUG, buf);
}

#endif							/* FDDEBUG */

static void
Delete(File file)
{
	Vfd		   *fileP;

	DO_DB(elog(DEBUG, "Delete %d (%s)",
			   file, VfdCache[file].fileName));
	DO_DB(_dump_lru());

	Assert(file != 0);

	fileP = &VfdCache[file];

	VfdCache[fileP->lruLessRecently].lruMoreRecently =
		VfdCache[file].lruMoreRecently;
	VfdCache[fileP->lruMoreRecently].lruLessRecently =
		VfdCache[file].lruLessRecently;

	DO_DB(_dump_lru());
}

static void
LruDelete(File file)
{
	Vfd		   *fileP;
	int			returnValue;

	DO_DB(elog(DEBUG, "LruDelete %d (%s)",
			   file, VfdCache[file].fileName));

	Assert(file != 0);

	fileP = &VfdCache[file];

	/* delete the vfd record from the LRU ring */
	Delete(file);

	/* save the seek position */
	fileP->seekPos = (long) lseek(fileP->fd, 0L, SEEK_CUR);
	Assert(fileP->seekPos != -1);

	/* if we have written to the file, sync it */
	if (fileP->fdstate & FD_DIRTY)
	{
		returnValue = fsync(fileP->fd);
		Assert(returnValue != -1);
		fileP->fdstate &= ~FD_DIRTY;
	}

	/* close the file */
	returnValue = close(fileP->fd);
	Assert(returnValue != -1);

	--nfile;
	fileP->fd = VFD_CLOSED;

}

static void
Insert(File file)
{
	Vfd		   *vfdP;

	DO_DB(elog(DEBUG, "Insert %d (%s)",
			   file, VfdCache[file].fileName));
	DO_DB(_dump_lru());

	vfdP = &VfdCache[file];

	vfdP->lruMoreRecently = 0;
	vfdP->lruLessRecently = VfdCache[0].lruLessRecently;
	VfdCache[0].lruLessRecently = file;
	VfdCache[vfdP->lruLessRecently].lruMoreRecently = file;

	DO_DB(_dump_lru());
}

static int
LruInsert(File file)
{
	Vfd		   *vfdP;
	int			returnValue;

	DO_DB(elog(DEBUG, "LruInsert %d (%s)",
			   file, VfdCache[file].fileName));

	vfdP = &VfdCache[file];

	if (FileIsNotOpen(file))
	{

		if (nfile >= pg_nofile())
			AssertLruRoom();

		/*
		 * Note, we check to see if there's a free file descriptor before
		 * attempting to open a file. One general way to do this is to try
		 * to open the null device which everybody should be able to open
		 * all the time. If this fails, we assume this is because there's
		 * no free file descriptors.
		 */
tryAgain:
		vfdP->fd = open(vfdP->fileName, vfdP->fileFlags, vfdP->fileMode);
		if (vfdP->fd < 0 && (errno == EMFILE || errno == ENFILE))
		{
			errno = 0;
			AssertLruRoom();
			goto tryAgain;
		}

		if (vfdP->fd < 0)
		{
			DO_DB(elog(DEBUG, "RE_OPEN FAILED: %d",
					   errno));
			return (vfdP->fd);
		}
		else
		{
			DO_DB(elog(DEBUG, "RE_OPEN SUCCESS"));
			++nfile;
		}

		/* seek to the right position */
		if (vfdP->seekPos != 0L)
		{
			returnValue =
				lseek(vfdP->fd, vfdP->seekPos, SEEK_SET);
			Assert(returnValue != -1);
		}

		/* init state on open */
		vfdP->fdstate = 0x0;

	}

	/*
	 * put it at the head of the Lru ring
	 */

	Insert(file);

	return (0);
}

static void
AssertLruRoom()
{
	DO_DB(elog(DEBUG, "AssertLruRoom. Opened %d", nfile));

	if (nfile <= 0)
		elog(FATAL, "AssertLruRoom: No opened files - no one can be closed");

	/*
	 * There are opened files and so there should be at least one used vfd
	 * in the ring.
	 */
	Assert(VfdCache[0].lruMoreRecently != 0);
	LruDelete(VfdCache[0].lruMoreRecently);
}

static File
AllocateVfd()
{
	Index		i;
	File		file;

	DO_DB(elog(DEBUG, "AllocateVfd. Size %d", SizeVfdCache));

	if (SizeVfdCache == 0)
	{

		/* initialize */
		VfdCache = (Vfd *) malloc(sizeof(Vfd));
		VfdCache->nextFree = 0;
		VfdCache->lruMoreRecently = 0;
		VfdCache->lruLessRecently = 0;
		VfdCache->fd = VFD_CLOSED;
		VfdCache->fdstate = 0x0;

		SizeVfdCache = 1;
	}

	if (VfdCache[0].nextFree == 0)
	{

		/*
		 * The free list is empty so it is time to increase the size of
		 * the array
		 */

		VfdCache = (Vfd *) realloc(VfdCache, sizeof(Vfd) * SizeVfdCache * 2);
		Assert(VfdCache != NULL);

		/*
		 * Set up the free list for the new entries
		 */

		for (i = SizeVfdCache; i < 2 * SizeVfdCache; i++)
		{
			MemSet((char *) &(VfdCache[i]), 0, sizeof(VfdCache[0]));
			VfdCache[i].nextFree = i + 1;
			VfdCache[i].fd = VFD_CLOSED;
		}

		/*
		 * Element 0 is the first and last element of the free list
		 */

		VfdCache[0].nextFree = SizeVfdCache;
		VfdCache[2 * SizeVfdCache - 1].nextFree = 0;

		/*
		 * Record the new size
		 */

		SizeVfdCache *= 2;
	}
	file = VfdCache[0].nextFree;

	VfdCache[0].nextFree = VfdCache[file].nextFree;

	return file;
}

static void
FreeVfd(File file)
{
	DO_DB(elog(DEBUG, "FreeVfd: %d (%s)",
			   file, VfdCache[file].fileName));

	VfdCache[file].nextFree = VfdCache[0].nextFree;
	VfdCache[0].nextFree = file;
}

/* filepath()
 * Open specified file name.
 * Fill in absolute path fields if necessary.
 *
 * Modify to use GetDatabasePath() rather than hardcoded paths.
 * - thomas 1997-11-02
 */
static char *
filepath(char *filename)
{
	char	   *buf;
	int			len;

	/* Not an absolute path name? Then fill in with database path... */
	if (*filename != SEP_CHAR)
	{
		len = strlen(GetDatabasePath()) + strlen(filename) + 2;
		buf = (char *) palloc(len);
		sprintf(buf, "%s%c%s", GetDatabasePath(), SEP_CHAR, filename);
	}
	else
	{
		buf = (char *) palloc(strlen(filename) + 1);
		strcpy(buf, filename);
	}

#ifdef FILEDEBUG
printf("filepath: path is %s\n", buf);
#endif

	return (buf);
}

static int
FileAccess(File file)
{
	int			returnValue;

	DO_DB(elog(DEBUG, "FileAccess %d (%s)",
			   file, VfdCache[file].fileName));

	/*
	 * Is the file open?  If not, close the least recently used, then open
	 * it and stick it at the head of the used ring
	 */

	if (FileIsNotOpen(file))
	{

		returnValue = LruInsert(file);
		if (returnValue != 0)
			return returnValue;

	}
	else
	{

		/*
		 * We now know that the file is open and that it is not the last
		 * one accessed, so we need to more it to the head of the Lru
		 * ring.
		 */

		Delete(file);
		Insert(file);
	}

	return (0);
}

/*
 *	Called when we get a shared invalidation message on some relation.
 */
#ifdef NOT_USED
void
FileInvalidate(File file)
{
	Assert(file > 0);
	if (!FileIsNotOpen(file))
	{
		LruDelete(file);
	}
}

#endif

/* VARARGS2 */
static File
fileNameOpenFile(FileName fileName,
				 int fileFlags,
				 int fileMode)
{
	File		file;
	Vfd		   *vfdP;

	DO_DB(elog(DEBUG, "fileNameOpenFile: %s %x %o",
			   fileName, fileFlags, fileMode));

	file = AllocateVfd();
	vfdP = &VfdCache[file];

	if (nfile >= pg_nofile())
		AssertLruRoom();

tryAgain:
	vfdP->fd = open(fileName, fileFlags, fileMode);
	if (vfdP->fd < 0 && (errno == EMFILE || errno == ENFILE))
	{
		DO_DB(elog(DEBUG, "fileNameOpenFile: not enough descs, retry, er= %d",
				   errno));
		errno = 0;
		AssertLruRoom();
		goto tryAgain;
	}

	vfdP->fdstate = 0x0;

	if (vfdP->fd < 0)
	{
		FreeVfd(file);
		return -1;
	}
	++nfile;
	DO_DB(elog(DEBUG, "fileNameOpenFile: success %d",
			   vfdP->fd));

	Insert(file);

	if (fileName == NULL)
	{
		elog(WARN, "fileNameOpenFile: NULL fname");
	}
	vfdP->fileName = malloc(strlen(fileName) + 1);
	strcpy(vfdP->fileName, fileName);

	vfdP->fileFlags = fileFlags & ~(O_TRUNC | O_EXCL);
	vfdP->fileMode = fileMode;
	vfdP->seekPos = 0;

	return file;
}

/*
 * open a file in the database directory ($PGDATA/base/...)
 */
File
FileNameOpenFile(FileName fileName, int fileFlags, int fileMode)
{
	File		fd;
	char	   *fname;

	fname = filepath(fileName);
	fd = fileNameOpenFile(fname, fileFlags, fileMode);
	pfree(fname);
	return (fd);
}

/*
 * open a file in an arbitrary directory
 */
File
PathNameOpenFile(FileName fileName, int fileFlags, int fileMode)
{
	return (fileNameOpenFile(fileName, fileFlags, fileMode));
}

void
FileClose(File file)
{
	int			returnValue;

	DO_DB(elog(DEBUG, "FileClose: %d (%s)",
			   file, VfdCache[file].fileName));

	if (!FileIsNotOpen(file))
	{

		/* remove the file from the lru ring */
		Delete(file);

		/* if we did any writes, sync the file before closing */
		if (VfdCache[file].fdstate & FD_DIRTY)
		{
			returnValue = fsync(VfdCache[file].fd);
			Assert(returnValue != -1);
			VfdCache[file].fdstate &= ~FD_DIRTY;
		}

		/* close the file */
		returnValue = close(VfdCache[file].fd);
		Assert(returnValue != -1);

		--nfile;
		VfdCache[file].fd = VFD_CLOSED;
	}

	/*
	 * Add the Vfd slot to the free list
	 */
	FreeVfd(file);

	/*
	 * Free the filename string
	 */
	free(VfdCache[file].fileName);
}

void
FileUnlink(File file)
{
	int			returnValue;

	DO_DB(elog(DEBUG, "FileUnlink: %d (%s)",
			   file, VfdCache[file].fileName));

	if (!FileIsNotOpen(file))
	{

		/* remove the file from the lru ring */
		Delete(file);

		/* if we did any writes, sync the file before closing */
		if (VfdCache[file].fdstate & FD_DIRTY)
		{
			returnValue = fsync(VfdCache[file].fd);
			Assert(returnValue != -1);
			VfdCache[file].fdstate &= ~FD_DIRTY;
		}

		/* close the file */
		returnValue = close(VfdCache[file].fd);
		Assert(returnValue != -1);

		--nfile;
		VfdCache[file].fd = VFD_CLOSED;
	}
	/* add the Vfd slot to the free list */
	FreeVfd(file);

	/* free the filename string */
	unlink(VfdCache[file].fileName);
	free(VfdCache[file].fileName);
}

int
FileRead(File file, char *buffer, int amount)
{
	int			returnCode;

	DO_DB(elog(DEBUG, "FileRead: %d (%s) %d %p",
			   file, VfdCache[file].fileName, amount, buffer));

	FileAccess(file);
	returnCode = read(VfdCache[file].fd, buffer, amount);
	if (returnCode > 0)
	{
		VfdCache[file].seekPos += returnCode;
	}

	return returnCode;
}

int
FileWrite(File file, char *buffer, int amount)
{
	int			returnCode;

	DO_DB(elog(DEBUG, "FileWrite: %d (%s) %d %p",
			   file, VfdCache[file].fileName, amount, buffer));

	FileAccess(file);
	returnCode = write(VfdCache[file].fd, buffer, amount);
	if (returnCode > 0)
	{							/* changed by Boris with Mao's advice */
		VfdCache[file].seekPos += returnCode;
	}

	/* record the write */
	VfdCache[file].fdstate |= FD_DIRTY;

	return returnCode;
}

long
FileSeek(File file, long offset, int whence)
{
	int			returnCode;

	DO_DB(elog(DEBUG, "FileSeek: %d (%s) %ld %d",
			   file, VfdCache[file].fileName, offset, whence));

	if (FileIsNotOpen(file))
	{
		switch (whence)
		{
			case SEEK_SET:
				VfdCache[file].seekPos = offset;
				return offset;
			case SEEK_CUR:
				VfdCache[file].seekPos = VfdCache[file].seekPos + offset;
				return VfdCache[file].seekPos;
			case SEEK_END:
				FileAccess(file);
				returnCode = VfdCache[file].seekPos =
					lseek(VfdCache[file].fd, offset, whence);
				return returnCode;
			default:
				elog(WARN, "FileSeek: invalid whence: %d", whence);
				break;
		}
	}
	else
	{
		returnCode = VfdCache[file].seekPos =
			lseek(VfdCache[file].fd, offset, whence);
		return returnCode;
	}
	/* NOTREACHED */
	return (-1L);
}

/*
 * XXX not actually used but here for completeness
 */
#ifdef NOT_USED
long
FileTell(File file)
{
	DO_DB(elog(DEBUG, "FileTell %d (%s)",
			   file, VfdCache[file].fileName));
	return VfdCache[file].seekPos;
}

#endif

int
FileTruncate(File file, int offset)
{
	int			returnCode;

	DO_DB(elog(DEBUG, "FileTruncate %d (%s)",
			   file, VfdCache[file].fileName));

	FileSync(file);
	FileAccess(file);
	returnCode = ftruncate(VfdCache[file].fd, offset);
	return (returnCode);
}

int
FileSync(File file)
{
	int			returnCode;

	/*
	 * If the file isn't open, then we don't need to sync it; we always
	 * sync files when we close them.  Also, if we haven't done any writes
	 * that we haven't already synced, we can ignore the request.
	 */

	if (VfdCache[file].fd < 0 || !(VfdCache[file].fdstate & FD_DIRTY))
	{
		returnCode = 0;
	}
	else
	{
		returnCode = fsync(VfdCache[file].fd);
		VfdCache[file].fdstate &= ~FD_DIRTY;
	}

	return returnCode;
}

int
FileNameUnlink(char *filename)
{
	int			retval;
	char	   *fname;

	fname = filepath(filename);
	retval = unlink(fname);
	pfree(fname);
	return (retval);
}

/*
 * if we want to be sure that we have a real file descriptor available
 * (e.g., we want to know this in psort) we call AllocateFile to force
 * availability.  when we are done we call FreeFile to deallocate the
 * descriptor.
 *
 * allocatedFiles keeps track of how many have been allocated so we
 * can give a warning if there are too few left.
 */
static int	allocatedFiles = 0;

FILE	   *
AllocateFile(char *name, char *mode)
{
	FILE	   *file;
	int			fdleft;

	DO_DB(elog(DEBUG, "AllocateFile: Allocated %d.", allocatedFiles));

TryAgain:
	if ((file = fopen(name, mode)) == NULL)
	{
		if (errno == EMFILE || errno == ENFILE)
		{
			DO_DB(elog(DEBUG, "AllocateFile: not enough descs, retry, er= %d",
					   errno));
			errno = 0;
			AssertLruRoom();
			goto TryAgain;
		}
	}
	else
	{
		++allocatedFiles;
		fdleft = pg_nofile() - allocatedFiles;
		if (fdleft < 6)
			elog(NOTICE, "warning: few usable file descriptors left (%d)", fdleft);
	}
	return file;
}

/*
 * XXX What happens if FreeFile() is called without a previous
 * AllocateFile()?
 */
void
FreeFile(FILE *file)
{
	DO_DB(elog(DEBUG, "FreeFile: Allocated %d.", allocatedFiles));

	Assert(allocatedFiles > 0);
	fclose(file);
	--allocatedFiles;
}

void
closeAllVfds()
{
	int			i;

	Assert(FileIsNotOpen(0));	/* Make sure ring not corrupted */
	for (i = 1; i < SizeVfdCache; i++)
	{
		if (!FileIsNotOpen(i))
			LruDelete(i);
	}
}
