fh_cache.c

/*
 * UNFS3 filehandle cache
 * (C) 2004
 * see file LICENSE for license details
 */

#include "config.h"

#include <sys/types.h>
#include <sys/stat.h>
#include <rpc/rpc.h>
#include <limits.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>

#include "nfs.h"
#include "fh.h"
#include "locate.h"
#include "fh_cache.h"
#include "mount.h"
#include "daemon.h"
#include "attr.h"
#include "Config/exports.h"
#include "backend.h"

/* number of entries in fh cache */
#define CACHE_ENTRIES	4096

typedef struct {
    uint32 dev;			/* device */
    uint64 ino;			/* inode */
    char path[NFS_MAXPATHLEN];	/* pathname */
    unsigned int use;		/* last use */
} unfs3_cache_t;

static unfs3_cache_t fh_cache[CACHE_ENTRIES];

/* statistics */
int fh_cache_max = 0;
int fh_cache_use = 0;
int fh_cache_hit = 0;

/* counter for LRU */
static unsigned int fh_cache_time = 0;

/*
 * last returned entry
 *
 * this entry must not be overwritten before the next lookup, because
 * operations such as CREATE may still be needing the path inside the
 * entry for getting directory attributes
 *
 * this is needed since fh_cache_time can roll around to 0, thus
 * making the entry evictable
 */
static int fh_last_entry = -1;

/*
 * return next pseudo-time value for LRU counter
 */
static unsigned int fh_cache_next(void)
{
    return ++fh_cache_time;
}

/*
 * initialize cache
 */
void fh_cache_init(void)
{
    memset(fh_cache, 0, sizeof(unfs3_cache_t) * CACHE_ENTRIES);
}

/*
 * find cache index to use for new entry
 * returns either an empty slot or the least recently used slot if no
 * empty slot is present
 */
static int fh_cache_lru(void)
{
    unsigned int best = UINT_MAX;
    int best_idx = 0;
    int i;

    /* if cache is not full, we simply hand out the next slot */
    if (fh_cache_max < CACHE_ENTRIES - 1)
	return fh_cache_max++;

    for (i = 0; i < CACHE_ENTRIES; i++) {
	if (i == fh_last_entry)
	    continue;
	if (fh_cache[i].use == 0)
	    return i;
	if (fh_cache[i].use < best) {
	    best = fh_cache[i].use;
	    best_idx = i;
	}
    }

    /* avoid stomping over last returned entry */
    if (best_idx == 0 && fh_last_entry == 0)
	best_idx = 1;

    return best_idx;
}

/*
 * invalidate (clear) a cache entry
 */
static void fh_cache_inval(int idx)
{
    fh_cache[idx].dev = 0;
    fh_cache[idx].ino = 0;
    fh_cache[idx].use = 0;
    fh_cache[idx].path[0] = 0;
}

/*
 * find index given device and inode number
 */
static int fh_cache_index(uint32 dev, uint64 ino)
{
    int i, res = -1;

    for (i = 0; i < fh_cache_max + 1; i++)
	if (fh_cache[i].dev == dev && fh_cache[i].ino == ino) {
	    res = i;
	    break;
	}

    return res;
}

/*
 * add an entry to the filehandle cache
 */
char *fh_cache_add(uint32 dev, uint64 ino, const char *path)
{
    int idx;

    /* if we already have a matching entry, overwrite that */
    idx = fh_cache_index(dev, ino);

    /* otherwise overwrite least recently used entry */
    if (idx == -1)
	idx = fh_cache_lru();

    fh_cache[idx].dev = dev;
    fh_cache[idx].ino = ino;
    fh_cache[idx].use = fh_cache_next();

    strcpy(fh_cache[idx].path, path);

    return fh_cache[idx].path;
}

/*
 * lookup an entry in the cache given a device, inode, and generation number
 */
static char *fh_cache_lookup(uint32 dev, uint64 ino)
{
    int i, res;
    backend_statstruct buf;

    i = fh_cache_index(dev, ino);

    if (i != -1) {
	/* check whether path to <dev,ino> relation still holds */
	res = backend_lstat(fh_cache[i].path, &buf);
	if (res == -1) {
	    /* object does not exist any more */
	    fh_cache_inval(i);
	    return NULL;
	}
	if (buf.st_dev == dev && buf.st_ino == ino) {
	    /* cache hit, update time on cache entry */
	    fh_cache[i].use = fh_cache_next();

	    /* update stat cache */
	    fix_dir_times(fh_cache[i].path, &buf);
	    st_cache_valid = TRUE;
	    st_cache = buf;

	    /* prevent next fh_cache_add from overwriting entry */
	    fh_last_entry = i;

	    return fh_cache[i].path;
	} else {
	    /* path to <dev,ino> relation has changed */
	    fh_cache_inval(i);
	    return NULL;
	}
    }

    return NULL;
}

/*
 * resolve a filename into a path
 * cache-using wrapper for fh_decomp_raw
 */
char *fh_decomp(nfs_fh3 fh)
{
    char *result;
    unfs3_fh_t obj = fh_decode(&fh);

    if (!nfh_valid(fh)) {
	st_cache_valid = FALSE;
	return NULL;
    }

    /* Does the fsid match some static fsid? */
    if ((result = export_point_from_fsid(obj.dev)) != NULL) {
	if (obj.ino == 0x1) {
	    /* This FH refers to the export point itself */
	    /* Need to fill stat cache */
	    st_cache_valid = TRUE;

	    if (backend_lstat(result, &st_cache) == -1) {
		/* export point does not exist. This probably means that we
		   are using autofs and no media is inserted. Fill stat cache 
		   with dummy information */
		st_cache.st_mode = S_IFDIR | S_IRWXU | S_IRWXG | S_IRWXO;
		st_cache.st_nlink = 2;
		st_cache.st_uid = 0;
		st_cache.st_gid = 0;
		st_cache.st_rdev = 0;
		st_cache.st_size = 4096;
		st_cache.st_blksize = 512;
		st_cache.st_blocks = 8;
		st_cache.st_atime = 0;
		st_cache.st_mtime = 0;
		st_cache.st_ctime = 0;
	    } else {
		/* Stat was OK, but make sure the values are sane. Supermount 
		   returns insane values when no media is inserted, for
		   example. */
		if (st_cache.st_nlink == 0)
		    st_cache.st_nlink = 1;
		if (st_cache.st_size == 0)
		    st_cache.st_size = 4096;
		if (st_cache.st_blksize == 0)
		    st_cache.st_blksize = 512;
		if (st_cache.st_blocks == 0)
		    st_cache.st_blocks = 8;
		fix_dir_times(result, &st_cache);
	    }

	    st_cache.st_dev = obj.dev;
	    st_cache.st_ino = 0x1;
	    return result;
	}
    }

    /* try lookup in cache, increase cache usage counter */
    result = fh_cache_lookup(obj.dev, obj.ino);
    fh_cache_use++;

    if (!result) {
	/* not found, resolve the hard way */
	result = fh_decomp_raw(&obj);

	/* if still not found, do full recursive search) */
	if (!result)
	    result = backend_locate_file(obj.dev, obj.ino);

	if (result)
	    /* add to cache for later use if resolution ok */
	    result = fh_cache_add(obj.dev, obj.ino, result);
	else
	    /* could not resolve in any way */
	    st_cache_valid = FALSE;
    } else
	/* found, update cache hit statistic */
	fh_cache_hit++;

    return result;
}

/*
 * compose a filehandle for a path
 * cache-using wrapper for fh_comp_raw
 * exports_options must be called before
 */
unfs3_fh_t fh_comp(const char *path, struct svc_req * rqstp, int need_dir)
{
    unfs3_fh_t res;

    res = fh_comp_raw(path, rqstp, need_dir);
    if (fh_valid(res))
	/* add to cache for later use */
	fh_cache_add(res.dev, res.ino, path);

    res.pwhash = export_password_hash;
    return res;
}

/*
 * return pointer to composed filehandle
 * wrapper for fh_comp
 */
unfs3_fh_t *fh_comp_ptr(const char *path, struct svc_req * rqstp,
			int need_dir)
{
    static unfs3_fh_t res;

    res = fh_comp(path, rqstp, need_dir);
    if (fh_valid(res))
	return &res;
    else
	return NULL;
}