xref: /titanic_44/usr/src/uts/common/fs/zev/zev_checksums.c (revision 6d08434eebcfac45213e38af01c64cf2559760d3)

#include <sys/zfs_events.h>
#include <sys/zev_checksums.h>
#include <sys/fs/zev.h>
#include <sys/zfs_znode.h>
#include <sys/sha1.h>
#include <sys/avl.h>
#include <sys/sysmacros.h>
#include <sys/fs/zev.h>
#include <sys/zfs_rlock.h>
#include <sys/list.h>

typedef struct zev_sig_cache_chksums_t {
	/* begin of key */
	uint64_t			offset_l1;
	/* end of key */
	avl_node_t			avl_node;
	uint8_t		sigs[ZEV_L1_SIZE/ZEV_L0_SIZE][SHA1_DIGEST_LENGTH];
} zev_sig_cache_chksums_t;

typedef struct zev_sig_cache_file_t {
	/* begin of key */
	uint64_t			guid;
	uint64_t			ino;
	uint64_t			gen;
	/* end of key */
	uint32_t			refcnt;
	list_node_t			lru_node;
	avl_node_t			avl_node;
	avl_tree_t			chksums;
} zev_sig_cache_file_t;

typedef struct zev_sig_cache_t {
	kmutex_t			mutex;
	uint64_t			cache_size;
	uint64_t			max_cache_size;
	uint64_t			hits;
	uint64_t			misses;
	list_t				lru;
	avl_tree_t			files;
} zev_sig_cache_t;

extern offset_t zfs_read_chunk_size;	/* tuneable from zfs_vnops.c */

static uint8_t all_zero_sig[SHA1_DIGEST_LENGTH] = {
	0x1c, 0xea, 0xf7, 0x3d, 0xf4, 0x0e, 0x53, 0x1d, 0xf3, 0xbf,
	0xb2, 0x6b, 0x4f, 0xb7, 0xcd, 0x95, 0xfb, 0x7b, 0xff, 0x1d
};

static uint8_t unknown_sig[SHA1_DIGEST_LENGTH] = {
	0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
	0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00
};

static zev_sig_cache_t	zev_sig_cache;

static int
zev_cache_file_cmp(const void *entry_a, const void *entry_b)
{
	const zev_sig_cache_file_t *a = entry_a;
	const zev_sig_cache_file_t *b = entry_b;

	if (a->guid < b->guid)
		return -1;
	if (a->guid > b->guid)
		return 1;
	if (a->ino < b->ino)
		return -1;
	if (a->ino > b->ino)
		return 1;
	if (a->gen < b->gen)
		return -1;
	if (a->gen > b->gen)
		return 1;
	return 0;
}

static int
zev_chksum_cache_cmp(const void *entry_a, const void *entry_b)
{
	const zev_sig_cache_chksums_t *a = entry_a;
	const zev_sig_cache_chksums_t *b = entry_b;

	if (a->offset_l1 < b->offset_l1)
		return -1;
	if (a->offset_l1 > b->offset_l1)
		return 1;
	return 0;
}

/* must be called with zev_sig_cache.mutex held */
static void
zev_chksum_cache_file_free(zev_sig_cache_file_t *file)
{
	zev_sig_cache_chksums_t *cs;
	void *c = NULL; /* cookie */

	/* remove from lru list */
	list_remove(&zev_sig_cache.lru, file);
	/* free resources */
	avl_remove(&zev_sig_cache.files, file);
	while ((cs = avl_destroy_nodes(&file->chksums, &c)) != NULL) {
		zev_sig_cache.cache_size -= sizeof(*cs);
		zev_free(cs, sizeof(*cs));
	}
	avl_destroy(&file->chksums);
	zev_free(file, sizeof(*file));
	zev_sig_cache.cache_size -= sizeof(*file);
}

void
zev_chksum_init(void)
{
	memset(&zev_sig_cache, 0, sizeof(zev_sig_cache));
	mutex_init(&zev_sig_cache.mutex, NULL, MUTEX_DRIVER, NULL);
	avl_create(&zev_sig_cache.files, zev_cache_file_cmp,
	           sizeof(zev_sig_cache_file_t),
	           offsetof(zev_sig_cache_file_t, avl_node));
	list_create(&zev_sig_cache.lru,
	            sizeof(zev_sig_cache_file_t),
	            offsetof(zev_sig_cache_file_t, lru_node));
	zev_sig_cache.max_cache_size = ZEV_CHKSUM_DEFAULT_CACHE_SIZE;
}

void
zev_chksum_fini(void)
{
	zev_sig_cache_file_t *file;

	mutex_destroy(&zev_sig_cache.mutex);
	while ((file = avl_first(&zev_sig_cache.files)) != NULL)
		zev_chksum_cache_file_free(file);
	list_destroy(&zev_sig_cache.lru);
	avl_destroy(&zev_sig_cache.files);
}

static zev_sig_cache_file_t *
zev_chksum_cache_file_get_and_hold(znode_t *zp)
{
	zev_sig_cache_file_t find_file;
	zev_sig_cache_file_t *file;
	avl_index_t where;

	find_file.guid =
		dsl_dataset_phys(zp->z_zfsvfs->z_os->os_dsl_dataset)->ds_guid;
	find_file.ino = zp->z_id;
	find_file.gen = zp->z_gen;

	mutex_enter(&zev_sig_cache.mutex);
	file = avl_find(&zev_sig_cache.files, &find_file, &where);
	if (!file) {
		file = zev_alloc(sizeof(*file));
		file->guid =
		    dsl_dataset_phys(zp->z_zfsvfs->z_os->os_dsl_dataset)->ds_guid;
		file->ino = zp->z_id;
		file->gen = zp->z_gen;
		file->refcnt = 0;
		avl_create(&file->chksums, zev_chksum_cache_cmp,
		           sizeof(zev_sig_cache_chksums_t),
		           offsetof(zev_sig_cache_chksums_t, avl_node));
		list_insert_head(&zev_sig_cache.lru, file);
		avl_insert(&zev_sig_cache.files, file, where);
		zev_sig_cache.cache_size += sizeof(*file);
	}
	file->refcnt++;
	mutex_exit(&zev_sig_cache.mutex);
	return file;
}

static void
zev_chksum_cache_file_release(zev_sig_cache_file_t *file)
{
	mutex_enter(&zev_sig_cache.mutex);

	/* We don't invalidate/free/destroy *file. Cache expiry does that */
	file->refcnt--;

	/* Move file to front of lru list */
	list_remove(&zev_sig_cache.lru, file);
	list_insert_head(&zev_sig_cache.lru, file);

	mutex_exit(&zev_sig_cache.mutex);
}

static  zev_sig_cache_chksums_t *
zev_chksum_cache_get_lv1_entry(zev_sig_cache_file_t *file, uint64_t off_l1)
{
	zev_sig_cache_chksums_t find_chksum;
	zev_sig_cache_chksums_t *cs;
	avl_index_t where;

	mutex_enter(&zev_sig_cache.mutex);

	find_chksum.offset_l1 = off_l1;
	cs = avl_find(&file->chksums, &find_chksum, &where);
	if (!cs) {
		cs = zev_zalloc(sizeof(*cs));
		cs->offset_l1 = off_l1;
		avl_insert(&file->chksums, cs, where);
		zev_sig_cache.cache_size += sizeof(*cs);
	}

	mutex_exit(&zev_sig_cache.mutex);

	return cs;
}

void
zev_chksum_stats(uint64_t *c_size, uint64_t *c_hits, uint64_t *c_misses)
{
	mutex_enter(&zev_sig_cache.mutex);
	*c_size = zev_sig_cache.cache_size;
	*c_hits = zev_sig_cache.hits;
	*c_misses = zev_sig_cache.misses;
	mutex_exit(&zev_sig_cache.mutex);
}

static void
zev_chksum_cache_invalidate(zev_sig_cache_file_t *file,
                            znode_t *zp,
                            zev_chksum_mode_t mode,
                            uint64_t off,
                            uint64_t len)
{
	zev_sig_cache_chksums_t find_chksum;
	zev_sig_cache_chksums_t *cs;
	int idx;
	uint64_t off_l1;
	uint64_t len_l1;
	uint64_t pos_l0;
	uint64_t pos_l1;

	mutex_enter(&zev_sig_cache.mutex);

	/* start of this megabyte */
	off_l1 = P2ALIGN(off, ZEV_L1_SIZE);

	if (len == 0) {
		/* truncate() to EOF */
		len_l1 = ZEV_L1_SIZE;
	} else {
		/* full megabytes */
		len_l1 = len + (off - off_l1);
		len_l1 = P2ROUNDUP(len_l1, ZEV_L1_SIZE);
	}

	for (pos_l1 = off_l1; pos_l1 < (off_l1+len_l1); pos_l1 += ZEV_L1_SIZE) {

		find_chksum.offset_l1 = pos_l1;
		cs = avl_find(&file->chksums, &find_chksum, NULL);
		if (!cs)
			continue;

		for (pos_l0 = MAX(pos_l1, P2ALIGN(off, ZEV_L0_SIZE));
		     pos_l0 < (pos_l1 + ZEV_L1_SIZE);
		     pos_l0 += ZEV_L0_SIZE){

			if ((len > 0) && (pos_l0 > (off + len - 1)))
				break;

			idx = (pos_l0 % ZEV_L1_SIZE) / ZEV_L0_SIZE;
			memcpy(cs->sigs[idx], unknown_sig, SHA1_DIGEST_LENGTH);
		}
	}

	if (len == 0) {
		/* truncate() to EOF -> invalidate all l1 sigs beyond EOF */
		while ((cs = avl_last(&file->chksums)) != NULL) {
			if (cs->offset_l1 < zp->z_size)
				break;
			avl_remove(&file->chksums, cs);
			zev_sig_cache.cache_size -= sizeof(*cs);
			zev_free(cs, sizeof(*cs));
		}
	}

	mutex_exit(&zev_sig_cache.mutex);
}

static int
zev_chksum_cache_get(uint8_t *dst,
                     zev_sig_cache_file_t *file,
                     zev_sig_cache_chksums_t *cs,
                     uint64_t off_l0)
{
	int idx;

	mutex_enter(&zev_sig_cache.mutex);

	idx = (off_l0 % ZEV_L1_SIZE) / ZEV_L0_SIZE;
	if (!memcmp(cs->sigs[idx], unknown_sig, SHA1_DIGEST_LENGTH)) {
		zev_sig_cache.misses++;
		mutex_exit(&zev_sig_cache.mutex);
		return ENOENT;
	}
	memcpy(dst, cs->sigs[idx], SHA1_DIGEST_LENGTH);
	zev_sig_cache.hits++;

	mutex_exit(&zev_sig_cache.mutex);
	return 0;
}

static void
zev_chksum_cache_put(uint8_t *sig,
                     zev_sig_cache_file_t *file,
                     zev_sig_cache_chksums_t *cs,
                     uint64_t off_l0)
{
	zev_sig_cache_file_t *f;
	zev_sig_cache_file_t *tmp;
	int idx;

	mutex_enter(&zev_sig_cache.mutex);

	if (zev_sig_cache.max_cache_size == 0) {
		/* cache disabled */
		mutex_exit(&zev_sig_cache.mutex);
		return;
	}

	/* expire entries until there's room in the cache */
	f = list_tail(&zev_sig_cache.lru);
	while (f && (zev_sig_cache.cache_size > zev_sig_cache.max_cache_size)){
		tmp = f;
		f = list_prev(&zev_sig_cache.lru, f);
		if (tmp->refcnt == 0)
			zev_chksum_cache_file_free(tmp);
	}

	idx = (off_l0 % ZEV_L1_SIZE) / ZEV_L0_SIZE;
	memcpy(cs->sigs[idx], sig, SHA1_DIGEST_LENGTH);

	mutex_exit(&zev_sig_cache.mutex);
	return;
}

/* verbatim from zfs_vnops.c (unfortunatly it's declared static, there) */
static int
mappedread(vnode_t *vp, int nbytes, uio_t *uio)
{
	znode_t *zp = VTOZ(vp);
	objset_t *os = zp->z_zfsvfs->z_os;
	int64_t	start, off;
	int len = nbytes;
	int error = 0;

	start = uio->uio_loffset;
	off = start & PAGEOFFSET;
	for (start &= PAGEMASK; len > 0; start += PAGESIZE) {
		page_t *pp;
		uint64_t bytes = MIN(PAGESIZE - off, len);

		if (pp = page_lookup(vp, start, SE_SHARED)) {
			caddr_t va;

			va = zfs_map_page(pp, S_READ);
			error = uiomove(va + off, bytes, UIO_READ, uio);
			zfs_unmap_page(pp, va);
			page_unlock(pp);
		} else {
			error = dmu_read_uio(os, zp->z_id, uio, bytes);
		}
		len -= bytes;
		off = 0;
		if (error)
			break;
	}
	return (error);
}

static int
zev_safe_read(znode_t *zp, char *buf, uint64_t off, uint64_t len)
{
	uio_t		uio;
	struct iovec	iov;
	ssize_t		n;
	ssize_t		nbytes;
	int		error = 0;
	vnode_t		*vp = ZTOV(zp);
	objset_t	*os = zp->z_zfsvfs->z_os;

	/* set up uio */

	iov.iov_base = buf;
	iov.iov_len = ZEV_L0_SIZE;

	uio.uio_iov = &iov;
	uio.uio_iovcnt = 1;
	uio.uio_segflg = (short)UIO_SYSSPACE;
	uio.uio_llimit = RLIM64_INFINITY;
	uio.uio_fmode = FREAD;
	uio.uio_extflg = UIO_COPY_DEFAULT;

	uio.uio_loffset = off;
	uio.uio_resid = len;

again:
	if (uio.uio_loffset >= zp->z_size)
		return EINVAL;

	/* don't read past EOF */
	n = MIN(uio.uio_resid, zp->z_size - uio.uio_loffset);

	/* this block was essentially copied from zfs_read() in zfs_vnops.c */
	while (n > 0) {
		nbytes = MIN(n, zfs_read_chunk_size -
		    P2PHASE(uio.uio_loffset, zfs_read_chunk_size));

		if (vn_has_cached_data(vp)) {
			error = mappedread(vp, nbytes, &uio);
		} else {
			error = dmu_read_uio(os, zp->z_id, &uio, nbytes);
		}
		if (error) {
			if (error == EINTR)
				goto again;
			/* convert checksum errors into IO errors */
			if (error == ECKSUM)
				error = SET_ERROR(EIO);
			break;
		}

		n -= nbytes;
	}

	if (error)
		return error;
	return len - uio.uio_resid;
}

static void
zev_l0_sig(uint8_t *sig, char *buf)
{
	SHA1_CTX	ctx;

	SHA1Init(&ctx);
	SHA1Update(&ctx, buf, ZEV_L0_SIZE);
	SHA1Final(sig, &ctx);
	return;
}

static void
zev_l0_blocksig(uint8_t *blk_sig, uint8_t *l0_sig, uint8_t block_no)
{
	SHA1_CTX	ctx;

	SHA1Init(&ctx);
	SHA1Update(&ctx, l0_sig, SHA1_DIGEST_LENGTH);
	SHA1Update(&ctx, &block_no, sizeof(block_no));
	SHA1Final(blk_sig, &ctx);
	return;
}

static void
zev_l1_add(uint8_t *sig_l1, uint8_t *sig_l0)
{
	int	i;
	int	s;
	int	carry = 0;

	for (i = SHA1_DIGEST_LENGTH - 1; i >= 0; --i) {
		s = sig_l1[i] + sig_l0[i] + carry;
		carry = s > 255 ? 1 : 0;
		sig_l1[i] = s & 0xff;
	}
}

static int
zev_get_result_buffer(zev_sig_t **buffer,
                      uint64_t *buffer_len,
                      uint64_t max_buffer_len,
                      znode_t *zp,
                      uint64_t off,
                      uint64_t len,
                      zev_chksum_mode_t mode)
{
	uint64_t	blk_start;
	uint64_t	blk_end;
	uint64_t	l0_blocks;
	uint64_t	l1_blocks;
	uint64_t	sigs;
	int buflen;

	/* calculate result set size: how many checksums will we provide? */

	ASSERT(len > 0 || (mode == zev_truncate && len == 0));

	if (len == 0) {
		/* truncate */
		l0_blocks = ((off % ZEV_L0_SIZE) == 0) ? 0 : 1;
		l1_blocks = ((off % ZEV_L1_SIZE) == 0) ? 0 : 1;
	} else {
		/* how many lv1 checksums do we update? */
		blk_start = off / ZEV_L1_SIZE;
		blk_end = (off + len - 1) / ZEV_L1_SIZE;
		l1_blocks = blk_end - blk_start + 1;
		/* how many lv0 checksums do we update? */
		blk_start = off / ZEV_L0_SIZE;
		blk_end = (off + len - 1) / ZEV_L0_SIZE;
		l0_blocks = blk_end - blk_start + 1;
	}

	sigs = l1_blocks + l0_blocks;
	if (sigs == 0) {
		*buffer = NULL;
		*buffer_len = 0;
		return 0;
	}

	buflen = sigs * sizeof(zev_sig_t);
	if (max_buffer_len && (buflen > max_buffer_len)) {
		*buffer = NULL;
		*buffer_len = 0;
		return ENOSPC;
	}
	*buffer_len = buflen;
	*buffer = zev_alloc(buflen);
	return 0;
}

static void
zev_append_sig(zev_sig_t *s, int level, uint64_t off, uint8_t *sig)
{
	s->level = level;
	s->block_offset = off;
	memcpy(s->value, sig, SHA1_DIGEST_LENGTH);
}

/*
 * Calculate all l0 and l1 checksums that are affected by the given range.
 *
 * This function assumes that the ranges it needs to read are already
 * range-locked.
 */
int
zev_get_checksums(zev_sig_t **result,
                  uint64_t *result_buf_len,
                  uint64_t *signature_cnt,
                  uint64_t max_result_len,
                  znode_t *zp,
                  uint64_t off,
                  uint64_t len,
                  zev_chksum_mode_t mode)
{
	uint64_t	off_l1;
	uint64_t	len_l1;
	uint64_t	pos_l1;
	uint64_t	pos_l0;
	char		*buf;
	int64_t		ret;
	uint8_t		sig_l0[SHA1_DIGEST_LENGTH];
	uint8_t		blk_sig_l0[SHA1_DIGEST_LENGTH];
	uint8_t		sig_l1[SHA1_DIGEST_LENGTH];
	uint8_t		l0_block_no;
	zev_sig_t	*sig;
	int		non_empty_l0_blocks;
	zev_sig_cache_file_t *file;
	zev_sig_cache_chksums_t *cs;

	/*
	 * Note: for write events, the callback is called via
	 *    zfs_write() -> zfs_log_write() -> zev_znode_write_cb()
	 *
	 * The transaction is not commited, yet.
	 *
	 * A write() syscall might be split into smaller chunks by zfs_write()
	 *
	 * zfs_write() has a range lock when this is called. (zfs_vnops.c:925)
	 * In zev mode, the range lock will encompass all data we need
	 * to calculate our checksums.
	 *
	 * The same is true for truncates with non-zero length. ("punch hole")
	 */

	ASSERT(len > 0 || (mode == zev_truncate && len == 0));
	*signature_cnt = 0;

	/*
	 * Under certain circumstances we need the first l0 block's
	 * checksum, because we didn't store it in the database and
	 * can't easily get it from userspace.  Not for this exact point
	 * in time, anyway.  So we cheat a little.
	 */
	if (mode == zev_truncate && len == 0 && off == 4096) {
		/*
		 * Normally, we'd report no checkums:
		 *  - no l0 sum, because no remaining l0 block is changed
		 *  - no l1 sum, because the file is now too short for l1 sums
		 * Let's pretend we changed the first l0 block, then.
		 * Luckily the entire file is range locked during truncate().
		 */
		off = 0;
		len = 4096;
	}

	/* start of this megabyte */
	off_l1 = P2ALIGN(off, ZEV_L1_SIZE);
	/* full megabytes */
	if (len == 0) {
		/* truncate(): we'll look at the last lv1 block, only. */
		len_l1 = ZEV_L1_SIZE;
	} else {
		len_l1 = len + (off - off_l1);
		len_l1 = P2ROUNDUP(len_l1, ZEV_L1_SIZE);
	}

	file = zev_chksum_cache_file_get_and_hold(zp);
	zev_chksum_cache_invalidate(file, zp, mode, off, len);
	buf = zev_alloc(ZEV_L0_SIZE);

	ret = zev_get_result_buffer(result, result_buf_len, max_result_len,
	                            zp, off, len, mode);
	if (ret) {
		zev_free(buf, ZEV_L0_SIZE);
		zev_chksum_cache_file_release(file);
		return ret;
	}
	if (*result == NULL) {
		/* we're done */
		zev_free(buf, ZEV_L0_SIZE);
		zev_chksum_cache_file_release(file);
		return 0;
	}
	sig = *result;

	for (pos_l1 = off_l1; pos_l1 < (off_l1+len_l1); pos_l1 += ZEV_L1_SIZE) {

		if (pos_l1 > zp->z_size) {
			cmn_err(CE_WARN, "zev_get_checksums: off+len beyond "
			        "EOF. Unexpected behaviour; please fix! "
				"off=%" PRIu64 ", len=%" PRIu64 ", "
			        "dataset='%s', inode=%" PRIu64, off, len,
				zp->z_zfsvfs->z_os->
			        os_dsl_dataset->ds_dir->dd_myname, zp->z_id);
			zev_free(*result, *result_buf_len);
			*result = NULL;
			zev_free(buf, ZEV_L0_SIZE);
			zev_chksum_cache_file_release(file);
			return EIO;
		}

		/*
		 * Since we have a reference to 'file' 'cs' can't be expired.
		 * Since our ranges are range locked, other threads woun't
		 * touch our checksum entries. (not even read them)
		 * Hence, we don't need to hold() or release() 'cs'.
		 */
		cs = zev_chksum_cache_get_lv1_entry(file, pos_l1);

		l0_block_no = 0;
		non_empty_l0_blocks = 0;
		bzero(sig_l1, sizeof(sig_l1));
		for (pos_l0 = pos_l1;
		     pos_l0 < (pos_l1 + ZEV_L1_SIZE);
		     pos_l0 += ZEV_L0_SIZE){

			if (pos_l0 >= zp->z_size)
				break;	/* EOF */

			if (zev_chksum_cache_get(sig_l0, file,cs,pos_l0) != 0) {

				/* signature is not cached, yet. */
				ret = zev_safe_read(zp, buf,
				                    pos_l0, ZEV_L0_SIZE);
				if (ret < 0) {
					zev_free(*result, *result_buf_len);
					zev_free(buf, ZEV_L0_SIZE);
					zev_chksum_cache_file_release(file);
					return ret;
				}
				/* pad buffer with zeros if necessary */
				if (ret < ZEV_L0_SIZE)
					bzero(buf + ret, ZEV_L0_SIZE - ret);

				/* calculate signature */
				zev_l0_sig(sig_l0, buf);

				zev_chksum_cache_put(sig_l0, file, cs, pos_l0);
			}

			if (!memcmp(sig_l0, all_zero_sig, SHA1_DIGEST_LENGTH)) {
				/* all-zero l0 block.  omit signature. */
				l0_block_no++;
				continue;
			}
			non_empty_l0_blocks++;
			zev_l0_blocksig(blk_sig_l0, sig_l0, l0_block_no);
			zev_l1_add(sig_l1, blk_sig_l0);

			if (((pos_l0 + ZEV_L0_SIZE - 1) >= off) &&
			    (pos_l0 <= (off + len - 1))) {
				zev_append_sig(sig++, 0, pos_l0, sig_l0);
			}

			l0_block_no++;
		}

		if (non_empty_l0_blocks && (zp->z_size > ZEV_L0_SIZE))
			zev_append_sig(sig++, 1, pos_l1, sig_l1);
	}

	*signature_cnt = ((char *)sig - (char *)*result) / sizeof(zev_sig_t);

	zev_free(buf, ZEV_L0_SIZE);
	zev_chksum_cache_file_release(file);
	return 0;
}

int
zev_ioc_get_signatures(intptr_t arg, int mode)
{
	zev_ioctl_get_signatures_t gs;
	file_t *fp;
	int ret = 0;
	znode_t *zp;
	zev_sig_t *sig_buf = NULL;
	uint64_t sig_buf_len;
	uint64_t sig_cnt = 0;
	uint64_t sig_len;
	char *dst;
	int range_locked = 0;
	rl_t *rl;
	ssize_t	lock_off;
	ssize_t lock_len;
	struct zfsvfs *zfsvfs = NULL;

	if (ddi_copyin((void *)arg, &gs, sizeof(gs), mode) != 0)
		return EFAULT;
	fp = getf(gs.zev_fd);
	if (fp == NULL)
		return EBADF;
	if (fp->f_vnode->v_vfsp->vfs_fstype != zfsfstype) {
		ret = EINVAL;
		goto out;
	}
	zp = VTOZ(fp->f_vnode);

	/* modified version of ZFS_ENTER() macro - we need to clean up fp */
	zfsvfs = zp->z_zfsvfs;
	rrm_enter_read(&zfsvfs->z_teardown_lock, FTAG);
	if (zp->z_zfsvfs->z_unmounted) {
		ret = EIO;
		goto out;
	}
	/* modified version of ZFS_VERIFY_ZP() macro */
	if (zp->z_sa_hdl == NULL) {
		ret = EIO;
		goto out;
	}

	if (fp->f_vnode->v_type != VREG) {
		ret = EINVAL;
		goto out;
	}
	if (gs.zev_offset >= zp->z_size) {
		ret = EINVAL;
		goto out;
	}

	/* range lock data */
	lock_off = P2ALIGN(gs.zev_offset, ZEV_L1_SIZE);
	lock_len = gs.zev_len + (gs.zev_offset - lock_off);
	lock_len = P2ROUNDUP(lock_len, ZEV_L1_SIZE);
	rl = zfs_range_lock(zp, lock_off, lock_len, RL_READER);
	range_locked = 1;

	/* get checksums */
	ret = zev_get_checksums(&sig_buf, &sig_buf_len, &sig_cnt,
	                        gs.zev_bufsize,
	                        zp, gs.zev_offset, gs.zev_len, zev_write);
	if (ret)
		goto out;

	/* copy to userland */
	sig_len = sig_cnt * sizeof(zev_sig_t);
	gs.zev_signature_cnt = sig_cnt;
	if (ddi_copyout(&gs, (void *)arg, sizeof(gs), mode) != 0) {
		ret = EFAULT;
		goto out;
	}
	if (sig_cnt && sig_buf) {
		dst = (char *)arg + sizeof(gs);
		if (ddi_copyout(sig_buf, (void *)dst, sig_len, mode) != 0) {
			ret = EFAULT;
			goto out;
		}
	}
out:
	if (sig_buf)
		zev_free(sig_buf, sig_buf_len);
	if (range_locked)
		zfs_range_unlock(rl);
	if (zfsvfs)
		ZFS_EXIT(zfsvfs);
	releasef(gs.zev_fd);
	return ret;
}

void
zev_symlink_checksum(zev_znode_symlink_t *rec, char *link)
{
	char buf[ZEV_L0_SIZE];

	memset(buf, 0, sizeof(buf));
	strcpy(buf, link);
	zev_l0_sig(rec->signature.value, buf);
	rec->signature.level = 0;
	rec->signature.block_offset = 0;
}


void
zev_create_checksum(zev_znode_create_t *rec, znode_t *zp)
{
	char buf[ZEV_L0_SIZE];
	vnode_t *vp;
	uint64_t rdev;

	vp = ZTOV(zp);
	if (vp->v_type == VBLK || vp->v_type == VCHR) {
		sa_lookup(zp->z_sa_hdl, SA_ZPL_RDEV(zp->z_zfsvfs),
		          &rdev, sizeof(rdev));
		memset(buf, 0, sizeof(buf));
		snprintf(buf, sizeof(buf), "%c%d,%d",
		         vp->v_type == VBLK ? 'b' : 'c',
		         getmajor(rdev),
		         getminor(rdev));
		zev_l0_sig(rec->signature.value, buf);
	} else {
		memset(rec->signature.value, 0, sizeof(rec->signature.value));
	}
	rec->signature.level = 0;
	rec->signature.block_offset = 0;
}