zircon/system/ulib/ftl/ftln/ftln_util.c

// Copyright 2018 The Fuchsia Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

#include <math.h>
#include <stdarg.h>
#include <string.h>
#include <zircon/compiler.h>

#include "ftl.h"
#include "ftlnp.h"

//
// Configuration.
//
// Legacy wear lag parameters. Unused except for measuring some
// statistics below.
//
#define WC_LIM0_LAG 190  // avg wear lag priority trigger
#define WC_LIM1_LAG 205  // periodic wear lag priority trigger
#define WC_LIM2_LAG 252  // constant wear lag priority trigger

// Global Variable Definitions
uint32_t FtlnLim0Lag = WC_LIM0_LAG;
uint32_t FtlnLim1Lag = WC_LIM1_LAG;
uint32_t FtlnLim2Lag = WC_LIM2_LAG;

// Local Function Definitions

//  format_ftl: Erase all non-free blocks
//
//       Input: ftl = pointer to FTL control block
//
//     Returns: 0 on success, -1 on error
//
static int format_ftl(FTLN ftl) {
  ui32 meta_block;

  // Get number of block that will hold the metapage.
  if (ftl->free_mpn == (ui32)-1)
    meta_block = FtlnLoWcFreeBlk(ftl);
  else
    meta_block = ftl->free_mpn / ftl->pgs_per_blk;

  // Write meta page, to indicate that format is in progress.
  memset(ftl->main_buf, 0xFF, ftl->page_size);
  if (FtlnMetaWr(ftl, CONT_FORMAT)) {
    return -1;
  }

  // Erase all map blocks, mark all blocks free, and reset the FTL.
  return FtlnFormat(ftl, meta_block);
}

// first_free_blk: Find the first free block, counting from block zero
//
//       Input: ftl = pointer to FTL control block
//
//     Returns: block number if successful, else (ui32)-1 if none free
//
static ui32 first_free_blk(CFTLN ftl) {
  ui32 b;

  // Search for first free block.
  for (b = 0;; ++b) {
    // Return error if no block is free.
    if (b == ftl->num_blks) {
      return (ui32)FsError2(FTL_NO_FREE_BLK, ENOSPC);
    }

    // If block is free, return its block number.
    if (IS_FREE(ftl->bdata[b]))
      return b;
  }
}

// Global Function Definitions

// FtlnReport: Callback function used by upper file system layer to
//              notify FTL of events
//
//      Inputs: vol = FTL handle
//              msg = event
//              ... = additional arguments
//
//     Returns: 0 or 1 (unformat()) for success, -1 on failure
//
int FtlnReport(void* vol, ui32 msg, ...) {
  FTLN ftl = vol;
  va_list ap;

  // Set errno and return -1 if fatal I/O error occurred.
  if (ftl->flags & FTLN_FATAL_ERR)
    return FsError2(NDM_EIO, EIO);

  // Handle event passed down from file system layer.
  switch (msg) {
    case FS_UNFORMAT: {
      ui32 b;

      // Return error if volume is mounted.
      if (ftl->flags & FTLN_MOUNTED) {
        return FsError2(FTL_MOUNTED, EEXIST);
      }

      // Format volume. Return -1 if error.
      if (format_ftl(ftl))
        return -1;

      // Erase every unerased block. Return -1 if error.
      for (b = 0; b < ftl->num_blks; ++b)
        if ((ftl->bdata[b] & ERASED_BLK_FLAG) == FALSE)
          if (FtlnEraseBlk(ftl, b))
            return -1;

      // Delete volume (both FTL and FS). Free its memory. Volume is
      // unmounted, so nothing to flush. Return value can be ignored.
      FtlnDelVol(ftl);

      // Return '1' for success.
      return 1;
    }

    case FS_FORMAT:
    case FS_FORMAT_RESET_WC: {
      // Format volume. Return -1 if error.
      if (format_ftl(ftl)) {
        ftl->logger.error(__FILE__, __LINE__, "FTL format failed.");
        return -1;
      }

      // Check if we're to equalize the wear counts (for benchmarking).
      if (msg == FS_FORMAT_RESET_WC) {
        ui32 b, avg_lag = 0;

        // Compute average wear count and assign to every block.
        for (b = 0; b < ftl->num_blks; ++b)
          avg_lag += ftl->blk_wc_lag[b];
        avg_lag /= ftl->num_blks;
        ftl->high_wc -= avg_lag;
        for (b = 0; b < ftl->num_blks; ++b)
          ftl->blk_wc_lag[b] = 0;
        ftl->wear_data.avg_wc_lag = ftl->wc_lag_sum = 0;
      }

      // Return success.
      return 0;
    }

    case FS_VCLEAN:
      return FtlnVclean(ftl);

    case FS_UNMOUNT:
      // Return error if not mounted.
      if ((ftl->flags & FTLN_MOUNTED) == FALSE)
        return FsError2(FTL_UNMOUNTED, ENOENT);

      // Clear the 'mounted' flag.
      ftl->flags &= ~FTLN_MOUNTED;
      __FALLTHROUGH;

    case FS_SYNC: {
      // Prepare to write all dirty map cache pages. Return -1 if err.
      if (FtlnRecCheck(ftl, 0))
        return -1;

      // Save all dirty map pages to flash. Return -1 if error.
      if (ftlmcFlushMap(ftl->map_cache))
        return -1;
      PfAssert(ftl->num_free_blks >= FTLN_MIN_FREE_BLKS);

#if INC_FTL_NDM_MLC
      // For MLC devices, advance free_vpn pointer so next volume page
      // write can't corrupt previously written valid page.
      FtlnMlcSafeFreeVpn(ftl);
#endif

      // If request was for sync, return success now.
      if (msg == FS_SYNC)
        return 0;

#if INC_ELIST
      // Check if there is not a current erased-block list.
      if (ftl->elist_blk == (ui32)-1) {
        ui32 b, n;

        // Count the number of erased free blocks.
        for (n = b = 0; b < ftl->num_blks; ++b)
          if (IS_ERASED(ftl->bdata[b]))
            ++n;

        // Only write erased list if more than 1 block is erased.
        if (n > 1) {
          ui32 wc, *lp, prior_free_mpn;
          ui32* end = (ui32*)(ftl->main_buf + ftl->page_size);

          // Save free map page number and force elist writes to begin
          // on first page of a free map block.
          prior_free_mpn = ftl->free_mpn;
          ftl->free_mpn = (ui32)-1;

          // Set pointer to write first entry on page.
          lp = (ui32*)(ftl->main_buf + FTLN_META_DATA_BEG);

          // Loop to find erased free blocks.
          for (b = 0;;) {
            if (IS_ERASED(ftl->bdata[b])) {
#if DEBUG_ELIST
              // Verify that this block is unwritten.
              FtlnCheckBlank(ftl, b);
#endif

              // Write block number and wear count of erased block.
              WR32_LE(b, lp);
              ++lp;
              wc = ftl->high_wc - ftl->blk_wc_lag[b];
              WR32_LE(wc, lp);
              ++lp;

              // If all blocks recorded, fill rest of page with -1.
              if (--n == 0)
                while (lp != end) {
                  WR32_LE(-1, lp);
                  ++lp;
                }

              // Check if page is full.
              if (lp == end) {
                // Write page of erased list data.
                if (FtlnMetaWr(ftl, ERASED_LIST))
                  return -1;

                // Break if all erased blocks have been recorded.
                if (n == 0)
                  break;

                // Reset pointer to write next entry on new page.
                lp = (ui32*)(ftl->main_buf + FTLN_META_DATA_BEG);

                // Assert not at block end. That requires 16B pages.
                PfAssert(ftl->free_mpn != (ui32)-1);
              }
            }

            // Check if no blocks left to test.
            if (++b == ftl->num_blks) {
              // If unwritten data in last page, write it now.
              if (lp != (ui32*)(ftl->main_buf + FTLN_META_DATA_BEG))
                if (FtlnMetaWr(ftl, ERASED_LIST))
                  return -1;

              // List is finished, break.
              break;
            }
          }

          // Save elist block number and restore free map page number.
          ftl->elist_blk = ftl->free_mpn / ftl->pgs_per_blk;
          ftl->bdata[ftl->elist_blk] = FREE_BLK_FLAG;
          ++ftl->num_free_blks;
          ftl->free_mpn = prior_free_mpn;
        }
      }
#endif  // INC_ELIST

      if (ftln_debug() > 1) {
        // Display FTL statistics.
        FtlnStats(ftl);
        FtlnBlkStats(ftl);
      }

      // Return success.
      return 0;
    }

    case FS_FLUSH_PAGE: {
      ui32 vpn, mpn;

      // Use the va_arg mechanism to get virtual page to be flushed.
      va_start(ap, msg);
      vpn = va_arg(ap, ui32);
      va_end(ap);

      // Check argument for validity.
      PfAssert(vpn < ftl->num_vpages);

      // Figure out MPN this page belongs to.
      mpn = vpn / ftl->mappings_per_mpg;

      // Flush MPN from cache. Return -1 if error.
      if (ftlmcFlushPage(ftl->map_cache, mpn))
        return -1;

#if INC_FTL_NDM_MLC
      // For MLC devices, advance free_vpn pointer so next volume page
      // write can't corrupt previously written valid page.
      FtlnMlcSafeFreeVpn(ftl);
#endif

      // Return success.
      return 0;
    }

    case FS_MARK_UNUSED: {
      ui32 ppn, count, past_end, vpn;

      // Use va_arg mechanism to get the starting page and number of
      // pages to be invalidated.
      va_start(ap, msg);
      vpn = va_arg(ap, ui32);
      count = va_arg(ap, ui32);
      va_end(ap);

      // Check arguments for validity.
      if (vpn + count > ftl->num_vpages)
        return -1;

      // Mark page(s) unused in FTL.
      for (past_end = vpn + count; vpn < past_end; ++vpn) {
        // Prepare to potentially write 1 map page. Return -1 if error.
        if (FtlnRecCheck(ftl, -1))
          return -1;

        // Retrieve physical page number for VPN. Return -1 if error.
        if (FtlnMapGetPpn(ftl, vpn, &ppn) < 0)
          return -1;

        // If unmapped, skip page.
        if (ppn == (ui32)-1)
          continue;

#if FS_ASSERT
        // Confirm no physical page number changes below.
        ftl->assert_no_recycle = TRUE;
#endif

        // Assign invalid value to VPN's physical page number and
        // decrement block's used page count.
        if (FtlnMapSetPpn(ftl, vpn, (ui32)-1))
          return -1;
        PfAssert(ftl->num_free_blks >= FTLN_MIN_FREE_BLKS);
        FtlnDecUsed(ftl, ppn, vpn);

#if FS_ASSERT
        // End check for no physical page number changes.
        ftl->assert_no_recycle = FALSE;
#endif
      }

      // Return success.
      return 0;
    }

    case FS_VSTAT: {
      vstat* buf;

      // Use the va_arg mechanism to get the vstat buffer.
      va_start(ap, msg);
      buf = (vstat*)va_arg(ap, void*);
      va_end(ap);

      // Get the garbage level.
      buf->garbage_level = FtlnGarbLvl(ftl);

      // Record high wear count.
      ftl->stats.wear_count = ftl->high_wc;

      // Save running count of number of flash pages written.
      ftl->fl_pg_writes += ftl->stats.write_page;

      // Get TargetFTL-NDM RAM usage.
      ftl->stats.ram_used = sizeof(struct ftln) + ftl->num_map_pgs * sizeof(ui32) + ftl->page_size +
                            ftl->eb_size * ftl->pgs_per_blk + ftlmcRAM(ftl->map_cache) +
                            ftl->num_blks * (sizeof(ui32) + sizeof(ui8));
      if (ftln_debug() > 1) {
        printf("TargetFTL-NDM RAM usage:\n");
        printf(" - sizeof(Ftln) : %u\n", (int)sizeof(FTLN));
        printf(" - tmp buffers  : %u\n", ftl->page_size + ftl->eb_size * ftl->pgs_per_blk);
        printf(" - map pages    : %u\n", ftl->num_map_pgs * 4);
        printf(" - map cache    : %u\n", ftlmcRAM(ftl->map_cache));
        printf(" - bdata[]      : %u\n", ftl->num_blks * (int)(sizeof(ui32) + sizeof(ui8)));
      }

      const int kNumBuckets = sizeof(buf->wear_histogram) / sizeof(ui32);
      PfAssert(kNumBuckets == 20);
      int rv = FtlnGetWearHistogram(ftl, kNumBuckets, buf->wear_histogram);
      PfAssert(rv == 0);

      buf->num_blocks = ftl->num_blks;

      // Set TargetFTL-NDM driver call counts and reset internal ones.
      buf->ndm = ftl->stats;
      memset(&ftl->stats, 0, sizeof(ftl_ndm_stats));

      // Return success.
      return 0;
    }

    // Similar to vstat but only counters are exported.
    case FS_COUNTERS: {
      // First argument should be a pointer towards a counter struct.
      va_start(ap, msg);
      FtlCounters* counters = (FtlCounters*)va_arg(ap, void*);
      va_end(ap);
      counters->wear_count = ftl->high_wc;
      return 0;
    }

    case FS_MOUNT:
      // Return error if already mounted. Else set mounted flag.
      if (ftl->flags & FTLN_MOUNTED)
        return FsError2(FTL_MOUNTED, EEXIST);
      ftl->flags |= FTLN_MOUNTED;

      if (ftln_debug() > 1) {
        // Display FTL statistics.
        FtlnStats(ftl);
        FtlnBlkStats(ftl);
      } else {
        printf("FTL: total blocks: %u, free blocks: %u\n", ftl->num_blks, ftl->num_free_blks);
      }

      // Return success.
      return 0;
  }

  // Return success.
  return 0;
}

#if INC_FTL_NDM_MLC
// FtlnMlcSafeFreeVpn: For MLC devices, ensure free_vpn pointer is
//              on a page whose pair is at a higher offset than the
//              last non-free page
//
//       Input: ftl = pointer to FTL control block
//
void FtlnMlcSafeFreeVpn(FTLN ftl) {
  // Only adjust MLC volumes for which volume free pointer is set.
  if (ftl->free_vpn != (ui32)-1) {
    ui32 pn = ndmPastPrevPair(ftl->ndm, ftl->free_vpn);

    if (ftln_debug() > 0) {
      printf("FtlnMlcSafeFreeVpn: old free = %u, new free = %u\n", ftl->free_vpn, pn);
    }
    ftl->free_vpn = pn;
  }
}
#endif  // INC_FTL_NDM_MLC

// FtlnEraseBlk: Erase a block, increment its wear count, and mark it
//               free and erased
//
//      Inputs: ftl = pointer to FTL control block
//              b = block to erase
//
//     Returns: 0 on success, -1 on error
//
int FtlnEraseBlk(FTLN ftl, ui32 b) {
  ui32 wc_lag, tb, ge_lim2_cnt = 0;

#if INC_ELIST
  // Check if list of erased blocks/wear counts exists.
  if (ftl->elist_blk != (ui32)-1) {
    ui32 eb = ftl->elist_blk;

    // Forget erased list block number.
    ftl->elist_blk = (ui32)-1;

    // If not this block, erase it - because its info is out-of-date.
    if (eb != b)
      if (FtlnEraseBlk(ftl, eb))
        return -1;
  }
#endif

  // Call driver to erase block. Return -1 if error.
  ++ftl->stats.erase_block;
  if (ndmEraseBlock(ftl->start_pn + b * ftl->pgs_per_blk, ftl->ndm)) {
    ftl->logger.error(__FILE__, __LINE__, "FTL failed to erase block %u.",
                      ftl->start_pn / ftl->pgs_per_blk + b);
    return FtlnFatErr(ftl);
  }

  // If not free, increment free blocks count. Mark free and erased.
  if (IS_FREE(ftl->bdata[b]) == FALSE)
    ++ftl->num_free_blks;
  ftl->bdata[b] = FREE_BLK_FLAG | ERASED_BLK_FLAG;

  // Check if block has a positive wear count lag.
  if (ftl->blk_wc_lag[b]) {
    // Decrement block's wear lag and the total wear lag sum.
    --ftl->blk_wc_lag[b];
    --ftl->wc_lag_sum;

    // Check if this block formerly had the maximum wear lag value.
    if (ftl->blk_wc_lag[b] + 1 == ftl->wear_data.cur_max_lag) {
      // Calculate new max lag. Count blocks w/lag over FtlnLim2Lag.
      ftl->wear_data.cur_max_lag = 0;
      for (tb = 0; tb < ftl->num_blks; ++tb) {
        wc_lag = ftl->blk_wc_lag[tb];
        if (ftl->wear_data.cur_max_lag < wc_lag)
          ftl->wear_data.cur_max_lag = (uint8_t)wc_lag;
        if (wc_lag > FtlnLim2Lag)
          ++ge_lim2_cnt;
      }
    }

    // Else block has highest wear. Adjust lag counts of other blocks.
  } else {
    // To prepare for its update, clear the current maximum lag value.
    ftl->wear_data.cur_max_lag = 0;

    // Check the wear lag of all other blocks.
    for (tb = 0; tb < ftl->num_blks; ++tb) {
      // Skip this block, leaving its wear count lag at zero.
      if (tb == b)
        continue;

      // Check if block's wear lag is less than the maximum value.
      if (ftl->blk_wc_lag[tb] < 0xFF) {
        // Update block's wear lag, the lag sum, and over lim2 count.
        wc_lag = ftl->blk_wc_lag[tb];
        ftl->blk_wc_lag[tb] = (uint8_t)++wc_lag;
        if (wc_lag > FtlnLim2Lag)
          ++ge_lim2_cnt;
        ++ftl->wc_lag_sum;

        // Else increment count of wear lag overflows.
      } else {
        ++ftl->wear_data.max_wc_over;
        ++ge_lim2_cnt;
      }

      // If new values, update current and lifetime high wear lag.
      wc_lag = ftl->blk_wc_lag[tb];
      if (ftl->wear_data.cur_max_lag < wc_lag)
        ftl->wear_data.cur_max_lag = (uint8_t)wc_lag;
    }

    // Increment the high wear count value.
    ++ftl->high_wc;
  }

  // Update lifetime max wear lag, avg lag, and over limit 2 count.
  if (ftl->wear_data.lft_max_lag < ftl->wear_data.cur_max_lag)
    ftl->wear_data.lft_max_lag = ftl->wear_data.cur_max_lag;
  if (ftl->wear_data.max_ge_lim2 < ge_lim2_cnt)
    ftl->wear_data.max_ge_lim2 = ge_lim2_cnt;
  ftl->wear_data.avg_wc_lag = ftl->wc_lag_sum / ftl->num_blks;

  // Return success.
  return 0;
}

// FtlnLoWcFreeBlk: Find the free block with the lowest wear count
//
//       Input: ftl = pointer to FTL control block
//
//     Returns: block number if successful, else (ui32)-1 if none free
//
ui32 FtlnLoWcFreeBlk(CFTLN ftl) {
  ui32 b, free_b, hi_lag;

  // Search for first free block. Return error if no block is free.
  free_b = first_free_blk(ftl);
  if (free_b == (ui32)-1)
    return free_b;

  // Want free block with lowest wear count (highest wear lag).
  hi_lag = ftl->blk_wc_lag[free_b];
  for (b = free_b + 1; b < ftl->num_blks; ++b) {
    if (IS_FREE(ftl->bdata[b]) == FALSE)
      continue;

    if (ftl->blk_wc_lag[b] > hi_lag) {
      free_b = b;
      hi_lag = ftl->blk_wc_lag[free_b];
    }
  }

  // Return block number.
  return free_b;
}

// FtlnHiWcFreeBlk: Find the free block with the highest wear count
//
//       Input: ftl = pointer to FTL control block
//
//     Returns: block number if successful, else (ui32)-1 if none free
//
ui32 FtlnHiWcFreeBlk(CFTLN ftl) {
  ui32 b, free_b, lo_lag;

  // Search for first free block. Return error if no block is free.
  free_b = first_free_blk(ftl);
  if (free_b == (ui32)-1)
    return free_b;

  // Want free block with highest wear count (lowest wear lag).
  lo_lag = ftl->blk_wc_lag[free_b];
  for (b = free_b + 1; b < ftl->num_blks; ++b) {
    if (IS_FREE(ftl->bdata[b]) == FALSE)
      continue;

    if (ftl->blk_wc_lag[b] < lo_lag) {
      free_b = b;
      lo_lag = ftl->blk_wc_lag[free_b];
    }
  }

  // Return block number.
  return free_b;
}

//  FtlnFormat: Erase all map blocks, mark all blocks free, and reset
//              the FTL (keeping wear offsets)
//
//      Inputs: ftl = pointer to FTL control block
//              meta_block = number of block holding the metapage
//
//     Returns: 0 on success, -1 on error
//
int FtlnFormat(FTLN ftl, ui32 meta_block) {
  ui32 b;

  PfAssert(meta_block < ftl->num_blks);
  // Erase all map blocks, except the one containing the metapage.
  for (b = 0; b < ftl->num_blks; ++b) {
    // Skip non-map blocks.
    if (!IS_MAP_BLK(ftl->bdata[b]))
      continue;

    // Skip block containing the metapage - this will be erased last.
    if (b == meta_block)
      continue;

    // Erase map block. Return -1 if error.
    if (FtlnEraseBlk(ftl, b))
      return -1;
  }

  // Erase the block holding the metapage: format finished!
  if (FtlnEraseBlk(ftl, meta_block))
    return -1;

  // Mark all non-erased blocks as free with zero read wear.
  for (b = 0; b < ftl->num_blks; ++b)
    if (!IS_FREE(ftl->bdata[b]))
      ftl->bdata[b] = FREE_BLK_FLAG;
  ftl->num_free_blks = ftl->num_blks;

  // Re-initialize volume state.
  FtlnStateRst(ftl);
  ftl->high_bc = 1;  // initial block count of unformatted volumes

  if (ftln_debug() > 0) {
    // Display FTL statistics.
    FtlnBlkStats(ftl);
  }

  // Return success.
  return 0;
}

// FtlnStateRst: Initialize volume state (except wear count offsets)
//
//       Input: ftl = pointer to FTL control block
//
void FtlnStateRst(FTLN ftl) {
  uint n;

  ftl->high_bc = 0;
  ftl->high_bc_mblk = ftl->resume_vblk = (ui32)-1;
  ftl->high_bc_mblk_po = 0;
  ftl->copy_end_found = FALSE;
  ftl->max_rc_blk = (ui32)-1;
  ftl->free_vpn = ftl->free_mpn = (ui32)-1;
#if INC_ELIST
  ftl->elist_blk = (ui32)-1;
#endif
  ftl->deferment = 0;
#if FS_ASSERT
  ftl->assert_no_recycle = FALSE;
#endif
  memset(ftl->spare_buf, 0xFF, ftl->pgs_per_blk * ftl->eb_size);
  for (n = 0; n < ftl->num_map_pgs; ++n)
    ftl->mpns[n] = (ui32)-1;
  ftlmcInit(ftl->map_cache);
}

// FtlnDecUsed: Decrement block used count for page no longer in-use
//
//      Inputs: ftl = pointer to FTL control block
//              pn = physical page number
//              vpn = virtual page number
//
void FtlnDecUsed(FTLN ftl, ui32 pn, ui32 vpn) {
  ui32 b = pn / ftl->pgs_per_blk;

  // Decrement block used count.
  PfAssert(NUM_USED(ftl->bdata[b]));
  PfAssert(!IS_FREE(ftl->bdata[b]));
  DEC_USED(ftl->bdata[b]);

  if (ftln_debug() > 0) {
    // Read page spare area and assert VPNs match.
    ++ftl->stats.read_spare;
    // Ignore errors here.
    if (ndmReadSpare(ftl->start_pn + pn, ftl->spare_buf, ftl->ndm) >= 0) {
      PfAssert(GET_SA_VPN(ftl->spare_buf) == vpn);
    }
  }
}  // lint !e818

//  FtlnFatErr: Process FTL-NDM fatal error
//
//       Input: ftl = pointer to FTL control block
//
//     Returns: -1
//
int FtlnFatErr(FTLN ftl) {
  ftl->flags |= FTLN_FATAL_ERR;
  return FsError2(NDM_EIO, EIO);
}

// FtlnGetWearData: Return FTL's wear data
//
//       Input: ftl = pointer to FTL control block
//
//     Returns: Copy of FTL's wear metrics
//
FtlWearData FtlnGetWearData(void* vol) {
  uint b, n, lag, num_vblks = 0, use_sum = 0;
  uint lag_sum_squared = 0, used_sum_squared = 0;
  FTLN ftl = vol;
  FtlWearData wear_data = ftl->wear_data;
  double d1, d2, d3, d4;

  // Loop over the block wear count lag array, calculating metrics.
  wear_data.lag_ge_lim1 = wear_data.lag_ge_lim0 = 0;
  for (b = 0; b < ftl->num_blks; ++b) {
    lag = ftl->blk_wc_lag[b];
    if (lag >= FtlnLim1Lag)
      ++wear_data.lag_ge_lim1;
    if (lag >= FtlnLim0Lag)
      ++wear_data.lag_ge_lim0;
    lag_sum_squared += lag * lag;

    // Finished if map block or free block.
    if (IS_MAP_BLK(ftl->bdata[b]) || IS_FREE(ftl->bdata[b]))
      continue;

    // Calculate values for used page standard deviation.
    n = NUM_USED(ftl->bdata[b]);
    use_sum += n;
    used_sum_squared += n * n;
    ++num_vblks;
  }

  // Calculate the average number of consecutive recycles.
  if (ftl->recycle_needed) {
    uint n;

    n = 100 * wear_data.recycle_cnt;
    n = n / ftl->recycle_needed;
    n = n + 5;
    n = n / 10;
    wear_data.avg_consec_rec = n;
  } else
    wear_data.avg_consec_rec = 0;

  // Calculate the current write amplification.
  if (ftl->vol_pg_writes) {
    uint n;

    n = ftl->fl_pg_writes + ftl->stats.write_page;
    n = 100 * n;
    n = n / ftl->vol_pg_writes;
    n = n + 5;
    n = n / 10;
    wear_data.write_amp_avg = n;
  } else
    wear_data.write_amp_avg = 0;

  // Calculate the standard deviation of the block wear lag.
  d1 = lag_sum_squared;
  d1 *= ftl->num_blks;
  d2 = ftl->wc_lag_sum;
  d2 *= ftl->wc_lag_sum;
  d3 = ftl->num_blks * (ftl->num_blks - 1);
  d4 = (d1 - d2) / d3;
  wear_data.lag_sd = sqrt(d4);

  // Calculate the standard deviation of used pages per block.
  d1 = used_sum_squared;
  d1 *= num_vblks;
  d2 = use_sum;
  d2 *= use_sum;
  d3 = num_vblks * (num_vblks - 1);
  d4 = (d1 - d2) / d3;
  wear_data.used_sd = sqrt(d4);

  // Return structure of metrics on wear data.
  return wear_data;
}

#if DEBUG_ELIST
// FtlnCheckBlank: Ensure the specified block is blank
//
//      Inputs: ftl = pointer to FTL control block
//              b = block number of block to check
//
void FtlnCheckBlank(FTLN ftl, ui32 b) {
  ui32 pn = b * ftl->pgs_per_blk;
  ui32 end = pn + ftl->pgs_per_blk;
  int rc;

  do {
    rc = ftl->page_check(pn, ftl->main_buf, ftl->spare_buf, ftl->ndm);
    PfAssert(rc == NDM_PAGE_ERASED);
  } while (++pn < end);
}
#endif  // DEBUG_ELIST