/*
 *	page.c
 *
 *	per-page conversion operations
 *
 *	Copyright (c) 2010-2012, PostgreSQL Global Development Group
 *	contrib/pg_upgrade/page.c
 */

#include "postgres.h"
#include "knl/knl_variable.h"

#include "pg_upgrade.h"

#include "storage/bufpage.h"

#ifdef PAGE_CONVERSION

static const char* getPageVersion(uint16* version, const char* pathName);
static pageCnvCtx* loadConverterPlugin(uint16 newPageVersion, uint16 oldPageVersion);

/*
 * setupPageConverter()
 *
 *	This function determines the PageLayoutVersion of the old cluster and
 *	the PageLayoutVersion of the new cluster.  If the versions differ, this
 *	function loads a converter plugin and returns a pointer to a pageCnvCtx
 *	object (in *result) that knows how to convert pages from the old format
 *	to the new format.	If the versions are identical, this function just
 *	returns a NULL pageCnvCtx pointer to indicate that page-by-page conversion
 *	is not required.
 *
 *	If successful this function sets *result and returns NULL.	If an error
 *	occurs, this function returns an error message in the form of an null-terminated
 *	string.
 */
const char* setupPageConverter(pageCnvCtx** result)
{
    uint16 oldPageVersion;
    uint16 newPageVersion;
    pageCnvCtx* converter = NULL;
    const char* msg = NULL;
    char dstName[MAXPGPATH];
    char srcName[MAXPGPATH];
    int nRet = 0;

    nRet = snprintf_s(
        dstName, sizeof(dstName), sizeof(dstName) - 1, "%s/global/%u", new_cluster.pgdata, new_cluster.pg_database_oid);
    securec_check_ss_c(nRet, "\0", "\0");
    nRet = snprintf_s(
        srcName, sizeof(srcName), sizeof(srcName) - 1, "%s/global/%u", old_cluster.pgdata, old_cluster.pg_database_oid);
    securec_check_ss_c(nRet, "\0", "\0");

    if ((msg = getPageVersion(&oldPageVersion, srcName)) != NULL)
        return msg;

    if ((msg = getPageVersion(&newPageVersion, dstName)) != NULL)
        return msg;

    /*
     * If the old cluster and new cluster use the same page layouts, then we
     * don't need a page converter.
     */
    if (newPageVersion == oldPageVersion) {
        *result = NULL;
        return NULL;
    }

    /*
     * The clusters use differing page layouts, see if we can find a plugin
     * that knows how to convert from the old page layout to the new page
     * layout.
     */

    if ((converter = loadConverterPlugin(newPageVersion, oldPageVersion)) == NULL)
        return "could not find plugin to convert from old page layout to new page layout";
    else {
        *result = converter;
        return NULL;
    }
}

/*
 * getPageVersion()
 *
 *	Retrieves the PageLayoutVersion for the given relation.
 *
 *	Returns NULL on success (and stores the PageLayoutVersion at *version),
 *	if an error occurs, this function returns an error message (in the form
 *	of a null-terminated string).
 */
static const char* getPageVersion(uint16* version, const char* pathName)
{
    int relfd;
    PageHeaderData page;
    ssize_t bytesRead;

    if ((relfd = open(pathName, O_RDONLY, 0)) < 0)
        return "could not open relation";

    if ((bytesRead = read(relfd, &page, sizeof(page))) != sizeof(page)) {
        close(relfd);
        return "could not read page header";
    }

    *version = PageGetPageLayoutVersion(&page);

    close(relfd);

    return NULL;
}

/*
 * loadConverterPlugin()
 *
 *	This function loads a page-converter plugin library and grabs a
 *	pointer to each of the (interesting) functions provided by that
 *	plugin.  The name of the plugin library is derived from the given
 *	newPageVersion and oldPageVersion.	If a plugin is found, this
 *	function returns a pointer to a pageCnvCtx object (which will contain
 *	a collection of plugin function pointers). If the required plugin
 *	is not found, this function returns NULL.
 */
static pageCnvCtx* loadConverterPlugin(uint16 newPageVersion, uint16 oldPageVersion)
{
    char pluginName[MAXPGPATH];
    void* plugin = NULL;
    int nRet = 0;

    /*
     * Try to find a plugin that can convert pages of oldPageVersion into
     * pages of newPageVersion.  For example, if we oldPageVersion = 3 and
     * newPageVersion is 4, we search for a plugin named:
     * plugins/convertLayout_3_to_4.dll
     */

    /*
     * FIXME: we are searching for plugins relative to the current directory,
     * we should really search relative to our own executable instead.
     */
    nRet = snprintf_s(pluginName,
        sizeof(pluginName),
        sizeof(pluginName) - 1,
        "./plugins/convertLayout_%d_to_%d%s",
        oldPageVersion,
        newPageVersion,
        DLSUFFIX);
    securec_check_ss_c(nRet, "\0", "\0");

    if ((plugin = pg_dlopen(pluginName)) == NULL)
        return NULL;
    else {
        pageCnvCtx* result = (pageCnvCtx*)pg_malloc(sizeof(*result));

        result->old.PageVersion = oldPageVersion;
        result->newm.PageVersion = newPageVersion;

        result->startup = (pluginStartup)pg_dlsym(plugin, "init");
        result->convertFile = (pluginConvertFile)pg_dlsym(plugin, "convertFile");
        result->convertPage = (pluginConvertPage)pg_dlsym(plugin, "convertPage");
        result->shutdown = (pluginShutdown)pg_dlsym(plugin, "fini");
        result->pluginData = NULL;

        /*
         * If the plugin has exported an initializer, go ahead and invoke it.
         */
        if (result->startup)
            result->startup(
                MIGRATOR_API_VERSION, &result->pluginVersion, newPageVersion, oldPageVersion, &result->pluginData);

        return result;
    }
}

#endif