/*-
 * See the file LICENSE for redistribution information.
 *
 * Copyright (c) 1996, 1997, 1998
 *      Sleepycat Software.  All rights reserved.
 */
#include "config.h"

#ifndef lint
static const char sccsid[] = "@(#)log_get.c     10.38 (Sleepycat) 10/3/98";
#endif /* not lint */

#ifndef NO_SYSTEM_INCLUDES
#include <sys/types.h>

#include <errno.h>
#include <string.h>
#include <unistd.h>
#endif

#include "db_int.h"
#include "shqueue.h"
#include "db_page.h"
#include "log.h"
#include "hash.h"
#include "common_ext.h"

/*
 * log_get --
 *      Get a log record.
 */
int
log_get(dblp, alsn, dbt, flags)
        DB_LOG *dblp;
        DB_LSN *alsn;
        DBT *dbt;
        u_int32_t flags;
{
        int ret;

        LOG_PANIC_CHECK(dblp);

        /* Validate arguments. */
        if (flags != DB_CHECKPOINT && flags != DB_CURRENT &&
            flags != DB_FIRST && flags != DB_LAST &&
            flags != DB_NEXT && flags != DB_PREV && flags != DB_SET)
                return (__db_ferr(dblp->dbenv, "log_get", 1));

        if (F_ISSET(dblp, DB_AM_THREAD)) {
                if (flags == DB_NEXT || flags == DB_PREV || flags == DB_CURRENT)
                        return (__db_ferr(dblp->dbenv, "log_get", 1));
                if (!F_ISSET(dbt, DB_DBT_USERMEM | DB_DBT_MALLOC))
                        return (__db_ferr(dblp->dbenv, "threaded data", 1));
        }

        LOCK_LOGREGION(dblp);

        /*
         * If we get one of the log's header records, repeat the operation.
         * This assumes that applications don't ever request the log header
         * records by LSN, but that seems reasonable to me.
         */
        ret = __log_get(dblp, alsn, dbt, flags, 0);
        if (ret == 0 && alsn->offset == 0) {
                switch (flags) {
                case DB_FIRST:
                        flags = DB_NEXT;
                        break;
                case DB_LAST:
                        flags = DB_PREV;
                        break;
                }
                ret = __log_get(dblp, alsn, dbt, flags, 0);
        }

        UNLOCK_LOGREGION(dblp);

        return (ret);
}

/*
 * __log_get --
 *      Get a log record; internal version.
 *
 * PUBLIC: int __log_get __P((DB_LOG *, DB_LSN *, DBT *, u_int32_t, int));
 */
int
__log_get(dblp, alsn, dbt, flags, silent)
        DB_LOG *dblp;
        DB_LSN *alsn;
        DBT *dbt;
        u_int32_t flags;
        int silent;
{
        DB_LSN nlsn;
        HDR hdr;
        LOG *lp;
        size_t len;
        ssize_t nr;
        int cnt, ret;
        char *np, *tbuf;
        const char *fail;
        void *p, *shortp;

        lp = dblp->lp;
        fail = np = tbuf = NULL;

        nlsn = dblp->c_lsn;
        switch (flags) {
        case DB_CHECKPOINT:
                nlsn = lp->chkpt_lsn;
                if (IS_ZERO_LSN(nlsn)) {
                        __db_err(dblp->dbenv,
        "log_get: unable to find checkpoint record: no checkpoint set.");
                        ret = ENOENT;
                        goto err2;
                }
                break;
        case DB_NEXT:                           /* Next log record. */
                if (!IS_ZERO_LSN(nlsn)) {
                        /* Increment the cursor by the cursor record size. */
                        nlsn.offset += dblp->c_len;
                        break;
                }
                /* FALLTHROUGH */
        case DB_FIRST:                          /* Find the first log record. */
                /* Find the first log file. */
                if ((ret = __log_find(dblp, 1, &cnt)) != 0)
                        goto err2;

                /*
                 * We may have only entered records in the buffer, and not
                 * yet written a log file.  If no log files were found and
                 * there's anything in the buffer, it belongs to file 1.
                 */
                if (cnt == 0)
                        cnt = 1;

                nlsn.file = cnt;
                nlsn.offset = 0;
                break;
        case DB_CURRENT:                        /* Current log record. */
                break;
        case DB_PREV:                           /* Previous log record. */
                if (!IS_ZERO_LSN(nlsn)) {
                        /* If at start-of-file, move to the previous file. */
                        if (nlsn.offset == 0) {
                                if (nlsn.file == 1 ||
                                    __log_valid(dblp, nlsn.file - 1, 0) != 0)
                                        return (DB_NOTFOUND);

                                --nlsn.file;
                                nlsn.offset = dblp->c_off;
                        } else
                                nlsn.offset = dblp->c_off;
                        break;
                }
                /* FALLTHROUGH */
        case DB_LAST:                           /* Last log record. */
                nlsn.file = lp->lsn.file;
                nlsn.offset = lp->lsn.offset - lp->len;
                break;
        case DB_SET:                            /* Set log record. */
                nlsn = *alsn;
                break;
        }

retry:
        /* Return 1 if the request is past end-of-file. */
        if (nlsn.file > lp->lsn.file ||
            (nlsn.file == lp->lsn.file && nlsn.offset >= lp->lsn.offset))
                return (DB_NOTFOUND);

        /* If we've switched files, discard the current fd. */
        if (dblp->c_lsn.file != nlsn.file && dblp->c_fd != -1) {
                (void)__os_close(dblp->c_fd);
                dblp->c_fd = -1;
        }

        /* If the entire record is in the in-memory buffer, copy it out. */
        if (nlsn.file == lp->lsn.file && nlsn.offset >= lp->w_off) {
                /* Copy the header. */
                p = lp->buf + (nlsn.offset - lp->w_off);
                memcpy(&hdr, p, sizeof(HDR));

                /* Copy the record. */
                len = hdr.len - sizeof(HDR);
                if ((ret = __db_retcopy(dbt, (u_int8_t *)p + sizeof(HDR),
                    len, &dblp->c_dbt.data, &dblp->c_dbt.ulen, NULL)) != 0)
                        goto err1;
                goto cksum;
        }

        /* Acquire a file descriptor. */
        if (dblp->c_fd == -1) {
                if ((ret = __log_name(dblp, nlsn.file,
                    &np, &dblp->c_fd, DB_RDONLY | DB_SEQUENTIAL)) != 0) {
                        fail = np;
                        goto err1;
                }
                __os_freestr(np);
                np = NULL;
        }

        /* Seek to the header offset and read the header. */
        if ((ret =
            __os_seek(dblp->c_fd, 0, 0, nlsn.offset, 0, SEEK_SET)) != 0) {
                fail = "seek";
                goto err1;
        }
        if ((ret = __os_read(dblp->c_fd, &hdr, sizeof(HDR), &nr)) != 0) {
                fail = "read";
                goto err1;
        }
        if (nr == sizeof(HDR))
                shortp = NULL;
        else {
                /* If read returns EOF, try the next file. */
                if (nr == 0) {
                        if (flags != DB_NEXT || nlsn.file == lp->lsn.file)
                                goto corrupt;

                        /* Move to the next file. */
                        ++nlsn.file;
                        nlsn.offset = 0;
                        goto retry;
                }

                /*
                 * If read returns a short count the rest of the record has
                 * to be in the in-memory buffer.
                 */
                if (lp->b_off < sizeof(HDR) - nr)
                        goto corrupt;

                /* Get the rest of the header from the in-memory buffer. */
                memcpy((u_int8_t *)&hdr + nr, lp->buf, sizeof(HDR) - nr);
                shortp = lp->buf + (sizeof(HDR) - nr);
        }

        /*
         * Check for buffers of 0's, that's what we usually see during
         * recovery, although it's certainly not something on which we
         * can depend.
         */
        if (hdr.len <= sizeof(HDR))
                goto corrupt;
        len = hdr.len - sizeof(HDR);

        /* If we've already moved to the in-memory buffer, fill from there. */
        if (shortp != NULL) {
                if (lp->b_off < ((u_int8_t *)shortp - lp->buf) + len)
                        goto corrupt;
                if ((ret = __db_retcopy(dbt, shortp, len,
                    &dblp->c_dbt.data, &dblp->c_dbt.ulen, NULL)) != 0)
                        goto err1;
                goto cksum;
        }

        /*
         * Allocate temporary memory to hold the record.
         *
         * XXX
         * We're calling malloc(3) with a region locked.  This isn't
         * a good idea.
         */
        if ((ret = __os_malloc(len, NULL, &tbuf)) != 0)
                goto err1;

        /*
         * Read the record into the buffer.  If read returns a short count,
         * there was an error or the rest of the record is in the in-memory
         * buffer.  Note, the information may be garbage if we're in recovery,
         * so don't read past the end of the buffer's memory.
         */
        if ((ret = __os_read(dblp->c_fd, tbuf, len, &nr)) != 0) {
                fail = "read";
                goto err1;
        }
        if (len - nr > sizeof(lp->buf))
                goto corrupt;
        if (nr != (ssize_t)len) {
                if (lp->b_off < len - nr)
                        goto corrupt;

                /* Get the rest of the record from the in-memory buffer. */
                memcpy((u_int8_t *)tbuf + nr, lp->buf, len - nr);
        }

        /* Copy the record into the user's DBT. */
        if ((ret = __db_retcopy(dbt, tbuf, len,
            &dblp->c_dbt.data, &dblp->c_dbt.ulen, NULL)) != 0)
                goto err1;
        __os_free(tbuf, 0);
        tbuf = NULL;

cksum:  if (hdr.cksum != __ham_func4(dbt->data, dbt->size)) {
                if (!silent)
                        __db_err(dblp->dbenv, "log_get: checksum mismatch");
                goto corrupt;
        }

        /* Update the cursor and the return lsn. */
        dblp->c_off = hdr.prev;
        dblp->c_len = hdr.len;
        dblp->c_lsn = *alsn = nlsn;

        return (0);

corrupt:/*
         * This is the catchall -- for some reason we didn't find enough
         * information or it wasn't reasonable information, and it wasn't
         * because a system call failed.
         */
        ret = EIO;
        fail = "read";

err1:   if (!silent)
                if (fail == NULL)
                        __db_err(dblp->dbenv, "log_get: %s", strerror(ret));
                else
                        __db_err(dblp->dbenv,
                            "log_get: %s: %s", fail, strerror(ret));
err2:   if (np != NULL)
                __os_freestr(np);
        if (tbuf != NULL)
                __os_free(tbuf, 0);
        return (ret);
}