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/*
* page.c
*
* per-page conversion operations
*
* Copyright (c) 2010-2011, PostgreSQL Global Development Group
* contrib/pg_upgrade/page.c
*/
#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;
const char *msg;
char dstName[MAXPGPATH];
char srcName[MAXPGPATH];
snprintf(dstName, sizeof(dstName), "%s/global/%u", new_cluster.pgdata,
new_cluster.pg_database_oid);
snprintf(srcName, sizeof(srcName), "%s/global/%u", old_cluster.pgdata,
old_cluster.pg_database_oid);
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 "can't 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 "can't open relation";
if ((bytesRead = read(relfd, &page, sizeof(page))) != sizeof(page))
{
close(relfd);
return "can't 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;
/*
* 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.
*/
snprintf(pluginName, sizeof(pluginName), "./plugins/convertLayout_%d_to_%d%s",
oldPageVersion, newPageVersion, DLSUFFIX);
if ((plugin = pg_dlopen(pluginName)) == NULL)
return NULL;
else
{
pageCnvCtx *result = (pageCnvCtx *) pg_malloc(sizeof(*result));
result->old.PageVersion = oldPageVersion;
result->new.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
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