/*      $NetBSD: offtab.c,v 1.15 2017/07/29 21:04:07 riastradh Exp $    */

/*-
* Copyright (c) 2014 The NetBSD Foundation, Inc.
* All rights reserved.
*
* This code is derived from software contributed to The NetBSD Foundation
* by Taylor R. Campbell.
*
* Redistribution and use in source and binary forms, with or without
* modification, are permitted provided that the following conditions
* are met:
* 1. Redistributions of source code must retain the above copyright
*    notice, this list of conditions and the following disclaimer.
* 2. Redistributions in binary form must reproduce the above copyright
*    notice, this list of conditions and the following disclaimer in the
*    documentation and/or other materials provided with the distribution.
*
* THIS SOFTWARE IS PROVIDED BY THE NETBSD FOUNDATION, INC. AND CONTRIBUTORS
* ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED
* TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
* PURPOSE ARE DISCLAIMED.  IN NO EVENT SHALL THE FOUNDATION OR CONTRIBUTORS
* BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
* CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
* SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
* INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
* CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
* ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
* POSSIBILITY OF SUCH DAMAGE.
*/

#include <sys/cdefs.h>
__RCSID("$NetBSD: offtab.c,v 1.15 2017/07/29 21:04:07 riastradh Exp $");

#include <sys/types.h>
#include <sys/endian.h>

#include <assert.h>
#include <err.h>
#include <errno.h>
#include <inttypes.h>
#include <limits.h>
#include <stdbool.h>
#include <stdlib.h>
#include <unistd.h>

#include "common.h"
#include "utils.h"

#include "offtab.h"

static void __printflike(1,2) __dead
offtab_bug(const char *fmt, ...)
{

       errx(1, "bug in offtab, please report");
}

static void __printflike(1,2) __dead
offtab_bugx(const char *fmt, ...)
{

       errx(1, "bug in offtab, please report");
}

static uint32_t
offtab_compute_window_size(struct offtab *offtab, uint32_t start)
{

       assert(start < offtab->ot_n_offsets);
       return MIN(offtab->ot_window_size, (offtab->ot_n_offsets - start));
}

static uint32_t
offtab_current_window_size(struct offtab *offtab)
{

       return offtab_compute_window_size(offtab, offtab->ot_window_start);
}

static uint32_t
offtab_current_window_end(struct offtab *offtab)
{

       assert(offtab->ot_window_start < offtab->ot_n_offsets);
       assert(offtab_current_window_size(offtab) <=
           (offtab->ot_n_offsets - offtab->ot_window_start));
       return (offtab->ot_window_start + offtab_current_window_size(offtab));
}

static void
offtab_compute_window_position(struct offtab *offtab, uint32_t window_start,
   size_t *bytes, off_t *pos)
{
       const uint32_t window_size = offtab_compute_window_size(offtab,
           window_start);

       __CTASSERT(MUL_OK(size_t, MAX_WINDOW_SIZE, sizeof(uint64_t)));
       *bytes = (window_size * sizeof(uint64_t));

       assert(window_start <= offtab->ot_n_offsets);
       __CTASSERT(MUL_OK(off_t, MAX_N_OFFSETS, sizeof(uint64_t)));
       const off_t window_offset = ((off_t)window_start *
           (off_t)sizeof(uint64_t));

       assert(offtab->ot_fdpos <= OFFTAB_MAX_FDPOS);
       __CTASSERT(ADD_OK(off_t, OFFTAB_MAX_FDPOS,
               (off_t)MAX_N_OFFSETS*sizeof(uint64_t)));
       assert(ADD_OK(off_t, offtab->ot_fdpos, window_offset));
       *pos = (offtab->ot_fdpos + window_offset);
}

#define OFFTAB_READ_SEEK        0x01
#define OFFTAB_READ_NOSEEK      0x00

static bool
offtab_read_window(struct offtab *offtab, uint32_t blkno, int read_flags)
{
       const uint32_t window_start = rounddown(blkno, offtab->ot_window_size);
       size_t window_bytes;
       off_t window_pos;

       assert(offtab->ot_mode == OFFTAB_MODE_READ);
       assert(ISSET(read_flags, OFFTAB_READ_SEEK) ||
           (lseek(offtab->ot_fd, 0, SEEK_CUR) == offtab->ot_fdpos) ||
           ((lseek(offtab->ot_fd, 0, SEEK_CUR) == -1) && (errno == ESPIPE)));

       offtab_compute_window_position(offtab, window_start,
           &window_bytes, &window_pos);
       const ssize_t n_read = (ISSET(read_flags, OFFTAB_READ_SEEK)
           ? pread_block(offtab->ot_fd, offtab->ot_window, window_bytes,
               window_pos)
           : read_block(offtab->ot_fd, offtab->ot_window, window_bytes));
       if (n_read == -1) {
               (*offtab->ot_report)("read offset table at %"PRIuMAX,
                   (uintmax_t)window_pos);
               return false;
       }
       assert(n_read >= 0);
       if ((size_t)n_read != window_bytes) {
               (*offtab->ot_reportx)("partial read of offset table"
                   " at %"PRIuMAX": %zu != %zu",
                   (uintmax_t)window_pos, (size_t)n_read, window_bytes);
               return false;
       }

       offtab->ot_window_start = window_start;

       return true;
}

static bool
offtab_maybe_read_window(struct offtab *offtab, uint32_t blkno, int read_flags)
{

       /* Don't bother if blkno is already in the window.  */
       if ((offtab->ot_window_start <= blkno) &&
           (blkno < offtab_current_window_end(offtab)))
               return true;

       if (!offtab_read_window(offtab, blkno, read_flags))
               return false;

       return true;
}

static void
offtab_write_window(struct offtab *offtab)
{
       size_t window_bytes;
       off_t window_pos;

       assert(offtab->ot_mode == OFFTAB_MODE_WRITE);

       offtab_compute_window_position(offtab, offtab->ot_window_start,
           &window_bytes, &window_pos);
       const ssize_t n_written = pwrite(offtab->ot_fd, offtab->ot_window,
           window_bytes, window_pos);
       if (n_written == -1)
               err_ss(1, "write initial offset table");
       assert(n_written >= 0);
       if ((size_t)n_written != window_bytes)
               errx_ss(1, "partial write of initial offset bytes: %zu <= %zu",
                   (size_t)n_written,
                   window_bytes);
}

static void
offtab_maybe_write_window(struct offtab *offtab, uint32_t start, uint32_t end)
{

       /* Don't bother if [start, end) does not cover our window.  */
       if (end <= offtab->ot_window_start)
               return;
       if (offtab_current_window_end(offtab) < start)
               return;

       offtab_write_window(offtab);
}

/*
* Initialize an offtab to support the specified number of offsets read
* to or written from fd at byte position fdpos.
*/
void
offtab_init(struct offtab *offtab, uint32_t n_offsets, uint32_t window_size,
   int fd, off_t fdpos)
{

       assert(offtab != NULL);
       assert(0 < n_offsets);
       assert(0 <= fd);
       assert(0 <= fdpos);
       assert(fdpos <= OFFTAB_MAX_FDPOS);

       offtab->ot_n_offsets = n_offsets;
       if ((window_size == 0) || (n_offsets < window_size))
               offtab->ot_window_size = n_offsets;
       else
               offtab->ot_window_size = window_size;
       assert(offtab->ot_window_size <= offtab->ot_n_offsets);
       offtab->ot_window_start = (uint32_t)-1;
       __CTASSERT(MUL_OK(size_t, MAX_WINDOW_SIZE, sizeof(uint64_t)));
       offtab->ot_window = malloc(offtab->ot_window_size * sizeof(uint64_t));
       if (offtab->ot_window == NULL)
               err(1, "malloc offset table");
       offtab->ot_blkno = (uint32_t)-1;
       offtab->ot_fd = fd;
       offtab->ot_fdpos = fdpos;
       offtab->ot_report = &offtab_bug;
       offtab->ot_reportx = &offtab_bugx;
       offtab->ot_mode = OFFTAB_MODE_NONE;
}

/*
* Destroy an offtab.
*/
void
offtab_destroy(struct offtab *offtab)
{

       free(offtab->ot_window);
}

/*
* For an offtab that has been used to read data from disk, convert it
* to an offtab that can be used to write subsequent data to disk.
* blkno is the last valid blkno read from disk.
*/
bool
offtab_transmogrify_read_to_write(struct offtab *offtab, uint32_t blkno)
{

       assert(offtab->ot_mode == OFFTAB_MODE_READ);
       assert(0 < blkno);

       if (!offtab_maybe_read_window(offtab, blkno, OFFTAB_READ_SEEK))
               return false;

       offtab->ot_mode = OFFTAB_MODE_WRITE;
       offtab->ot_blkno = blkno;

       return true;
}

/*
* Reset an offtab for reading an offset table from the beginning.
* Initializes in-memory state and may read data from offtab->ot_fd,
* which must currently be at byte position offtab->ot_fdpos.  Failure
* will be reported by the report/reportx routines, which are called
* like warn/warnx.  May fail; returns true on success, false on
* failure.
*
* This almost has copypasta of offtab_prepare_get, but this uses read,
* rather than pread, so that it will work on nonseekable input if the
* window is the whole offset table.
*/
bool
offtab_reset_read(struct offtab *offtab,
   void (*report)(const char *, ...) __printflike(1,2),
   void (*reportx)(const char *, ...) __printflike(1,2))
{

       assert((lseek(offtab->ot_fd, 0, SEEK_CUR) == offtab->ot_fdpos) ||
           ((lseek(offtab->ot_fd, 0, SEEK_CUR) == -1) && (errno == ESPIPE)));

       offtab->ot_report = report;
       offtab->ot_reportx = reportx;
       offtab->ot_mode = OFFTAB_MODE_READ;
       offtab->ot_blkno = (uint32_t)-1;

       if (!offtab_read_window(offtab, 0, OFFTAB_READ_NOSEEK))
               return false;

       if (offtab->ot_window_size < offtab->ot_n_offsets) {
               __CTASSERT(MUL_OK(off_t, MAX_N_OFFSETS, sizeof(uint64_t)));
               const off_t offtab_bytes = ((off_t)offtab->ot_n_offsets *
                   (off_t)sizeof(uint64_t));
               assert(offtab->ot_fdpos <= OFFTAB_MAX_FDPOS);
               __CTASSERT(ADD_OK(off_t, OFFTAB_MAX_FDPOS,
                       (off_t)MAX_N_OFFSETS*sizeof(uint64_t)));
               assert(ADD_OK(off_t, offtab->ot_fdpos, offtab_bytes));
               const off_t first_offset = (offtab->ot_fdpos + offtab_bytes);
               if (lseek(offtab->ot_fd, first_offset, SEEK_SET) == -1) {
                       (*offtab->ot_report)("lseek to first offset 0x%"PRIx64,
                           first_offset);
                       return false;
               }
       }

       return true;
}

/*
* Do any I/O or bookkeeping necessary to fetch the offset for blkno in
* preparation for a call to offtab_get.  May fail; returns true on
* success, false on failure.
*/
bool
offtab_prepare_get(struct offtab *offtab, uint32_t blkno)
{

       assert(offtab->ot_mode == OFFTAB_MODE_READ);
       assert(blkno < offtab->ot_n_offsets);

       if (!offtab_maybe_read_window(offtab, blkno, OFFTAB_READ_SEEK))
               return false;

       assert(offtab->ot_window_start <= blkno);
       assert(blkno < offtab_current_window_end(offtab));

       offtab->ot_blkno = blkno;
       return true;
}

/*
* Return the offset for blkno.  Caller must have called
* offtab_prepare_get beforehand.
*/
uint64_t
offtab_get(struct offtab *offtab, uint32_t blkno)
{

       assert(offtab->ot_mode == OFFTAB_MODE_READ);
       assert(blkno == offtab->ot_blkno);
       assert(offtab->ot_window_start <= blkno);
       assert(blkno < offtab_current_window_end(offtab));

       return be64toh(offtab->ot_window[blkno - offtab->ot_window_start]);
}

/*
* Reset offtab for writing a fresh offset table.  Initializes
* in-memory state and writes an empty offset table to offtab->ot_fd,
* which must currently be at byte position offtab->ot_fdpos.  May
* fail; returns on success, aborts with err(3) on failure.
*/
void
offtab_reset_write(struct offtab *offtab)
{
       uint32_t i;

       assert(lseek(offtab->ot_fd, 0, SEEK_CUR) == offtab->ot_fdpos);

       offtab->ot_mode = OFFTAB_MODE_WRITE;
       offtab->ot_blkno = (uint32_t)-1;

       /*
        * Initialize the offset table to all ones (except for the
        * fixed first offset) so that we can easily detect where we
        * were interrupted if we want to restart.
        */
       __CTASSERT(MAX_N_OFFSETS <= UINT32_MAX);
       assert(offtab->ot_n_offsets > 0);

       /* Initialize window of all ones.  */
       for (i = 0; i < offtab->ot_window_size; i++)
               offtab->ot_window[i] = ~(uint64_t)0;

       /* Write the window to every position in the table.  */
       const uint32_t n_windows =
           howmany(offtab->ot_n_offsets, offtab->ot_window_size);
       for (i = 1; i < n_windows; i++) {
               /* Change the start but reuse the all-ones buffer.  */
               offtab->ot_window_start = (i * offtab->ot_window_size);
               offtab_write_window(offtab);
       }

       /* Compute the number of bytes in the offset table.  */
       __CTASSERT(MUL_OK(off_t, MAX_N_OFFSETS, sizeof(uint64_t)));
       const off_t offtab_bytes = ((off_t)offtab->ot_n_offsets *
           sizeof(uint64_t));

       /* Compute the offset of the first block.  */
       assert(offtab->ot_fdpos <= OFFTAB_MAX_FDPOS);
       __CTASSERT(ADD_OK(off_t, OFFTAB_MAX_FDPOS,
               MAX_N_OFFSETS*sizeof(uint64_t)));
       assert(ADD_OK(off_t, offtab->ot_fdpos, offtab_bytes));
       const off_t first_offset = (offtab->ot_fdpos + offtab_bytes);

       /* Assert that it fits in 64 bits.  */
       __CTASSERT(MUL_OK(uint64_t, MAX_N_OFFSETS, sizeof(uint64_t)));
       __CTASSERT(ADD_OK(uint64_t, OFFTAB_MAX_FDPOS,
               (uint64_t)MAX_N_OFFSETS*sizeof(uint64_t)));

       /* Write out the first window with the first offset.  */
       offtab->ot_window_start = 0;
       offtab->ot_window[0] = htobe64((uint64_t)first_offset);
       offtab_write_window(offtab);

       if (lseek(offtab->ot_fd, first_offset, SEEK_SET) == -1)
               err(1, "lseek to first offset failed");
}

/*
* Guarantee that the disk reflects block offsets [0, n_offsets).  If
* OFFTAB_CHECKPOINT_SYNC is set in flags, will also fsync the entire
* offset table.  May fail; returns on success, aborts with err(3) on
* failure.  Fsync failure is considered success but is reported with a
* warning.
*
* This routine does not write state in memory, and does not read state
* that is not signal-safe.  The only state read is offtab->ot_window,
* offtab->ot_window_start, and quantities that are static for the
* signal-interruptable existence of the offset table.
*/
void
offtab_checkpoint(struct offtab *offtab, uint32_t n_offsets, int flags)
{

       assert(offtab->ot_mode == OFFTAB_MODE_WRITE);
       assert(n_offsets <= offtab->ot_n_offsets);

       /*
        * Write the window unless we just did that and were
        * interrupted before we could move the window.
        */
       if (offtab->ot_window != NULL)
               offtab_maybe_write_window(offtab, 0, n_offsets);

       if (ISSET(flags, OFFTAB_CHECKPOINT_SYNC)) {
               __CTASSERT(MUL_OK(off_t, MAX_N_OFFSETS, sizeof(uint64_t)));
               const off_t sync_bytes = ((off_t)n_offsets *
                   (off_t)sizeof(uint64_t));
               __CTASSERT(ADD_OK(off_t, OFFTAB_MAX_FDPOS,
                       MAX_N_OFFSETS*sizeof(uint64_t)));
               assert(ADD_OK(off_t, offtab->ot_fdpos, sync_bytes));
               if (fsync_range(offtab->ot_fd, (FFILESYNC | FDISKSYNC),
                       offtab->ot_fdpos, (offtab->ot_fdpos + sync_bytes))
                   == -1)
                       warn_ss("fsync of offset table failed");
       }
}

/*
* Do any I/O or bookkeeping necessary to set an offset for blkno.  May
* fail; returns on success, aborts with err(3) on failure.
*/
void
offtab_prepare_put(struct offtab *offtab, uint32_t blkno)
{
       uint32_t i;

       assert(offtab->ot_mode == OFFTAB_MODE_WRITE);
       assert(blkno < offtab->ot_n_offsets);

       /*
        * Assume, for convenience, that we write blocks in order.
        * Thus we need not do another read -- we can just clear the
        * window.
        */
       assert((offtab->ot_blkno == (uint32_t)-1) ||
           ((offtab->ot_blkno + 1) == blkno));

       /* If it's already in our window, we're good to go.  */
       if ((offtab->ot_window_start <= blkno) &&
           (blkno < offtab_current_window_end(offtab)))
               goto win;

       /* Otherwise, write out the current window and choose a new one.  */
       offtab_write_window(offtab);

       assert(offtab->ot_window_size <= blkno);
       assert(offtab->ot_window_start == (blkno - offtab->ot_window_size));
       assert((offtab->ot_window_start + offtab->ot_window_size) ==
           rounddown(blkno, offtab->ot_window_size));

   {
       uint64_t *window;
       sigset_t sigmask;

       /*
        * Mark the window as being updated so nobody tries to write it
        * (since we just wrote it) while we fill it with ones.
        */
       block_signals(&sigmask);
       window = offtab->ot_window;
       offtab->ot_window = NULL;
       restore_sigmask(&sigmask);

       /* Fill the window with ones.  */
       for (i = 0; i < offtab_current_window_size(offtab); i++)
               window[i] = ~(uint64_t)0;

       /* Restore the window as ready again.  */
       block_signals(&sigmask);
       offtab->ot_window = window;
       offtab->ot_window_start = rounddown(blkno, offtab->ot_window_size);
       restore_sigmask(&sigmask);
   }

win:    assert(offtab->ot_window_start <= blkno);
       assert(blkno < offtab_current_window_end(offtab));

       offtab->ot_blkno = blkno;
}

/*
* Actually set the offset for blkno.
*/
void
offtab_put(struct offtab *offtab, uint32_t blkno, uint64_t offset)
{

       assert(offtab->ot_mode == OFFTAB_MODE_WRITE);
       assert(blkno == offtab->ot_blkno);
       assert(offtab->ot_window_start <= blkno);
       assert(blkno < offtab_current_window_end(offtab));

       offtab->ot_window[blkno - offtab->ot_window_start] = htobe64(offset);
}

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