Add pg_ls_tmpdir function

This lists the contents of a temporary directory associated to a given
tablespace, useful to get information about on-disk consumption caused
by temporary files used by a session query.  By default, pg_default is
scanned, and a tablespace can be specified as argument.

This function is intended to be used by monitoring tools, and, unlike
pg_ls_dir(), access to them can be granted to non-superusers so that
those monitoring tools can observe the principle of least privilege.
Access is also given by default to members of pg_monitor.

Author: Nathan Bossart
Reviewed-by: Laurenz Albe
Discussion: https://postgr.es/m/92F458A2-6459-44B8-A7F2-2ADD3225046A@amazon.com

1 files changed, 55 insertions, 7 deletions

diff --git a/src/backend/utils/adt/genfile.c b/src/backend/utils/adt/genfile.c
index a97cbea2483..85bea8d5022 100644
--- a/src/backend/utils/adt/genfile.c
+++ b/src/backend/utils/adt/genfile.c
@@ -23,6 +23,7 @@
 #include "access/htup_details.h"
 #include "access/xlog_internal.h"
 #include "catalog/pg_authid.h"
+#include "catalog/pg_tablespace_d.h"
 #include "catalog/pg_type.h"
 #include "funcapi.h"
 #include "mb/pg_wchar.h"
@@ -31,6 +32,7 @@
 #include "storage/fd.h"
 #include "utils/builtins.h"
 #include "utils/memutils.h"
+#include "utils/syscache.h"
 #include "utils/timestamp.h"
 
 typedef struct
@@ -520,7 +522,7 @@ pg_ls_dir_1arg(PG_FUNCTION_ARGS)
 
 /* Generic function to return a directory listing of files */
 static Datum
-pg_ls_dir_files(FunctionCallInfo fcinfo, const char *dir)
+pg_ls_dir_files(FunctionCallInfo fcinfo, const char *dir, bool missing_ok)
 {
 	FuncCallContext *funcctx;
 	struct dirent *de;
@@ -549,10 +551,18 @@ pg_ls_dir_files(FunctionCallInfo fcinfo, const char *dir)
 		fctx->dirdesc = AllocateDir(fctx->location);
 
 		if (!fctx->dirdesc)
-			ereport(ERROR,
-					(errcode_for_file_access(),
-					 errmsg("could not open directory \"%s\": %m",
-							fctx->location)));
+		{
+			if (missing_ok && errno == ENOENT)
+			{
+				MemoryContextSwitchTo(oldcontext);
+				SRF_RETURN_DONE(funcctx);
+			}
+			else
+				ereport(ERROR,
+						(errcode_for_file_access(),
+						 errmsg("could not open directory \"%s\": %m",
+								fctx->location)));
+		}
 
 		funcctx->user_fctx = fctx;
 		MemoryContextSwitchTo(oldcontext);
@@ -601,12 +611,50 @@ pg_ls_dir_files(FunctionCallInfo fcinfo, const char *dir)
 Datum
 pg_ls_logdir(PG_FUNCTION_ARGS)
 {
-	return pg_ls_dir_files(fcinfo, Log_directory);
+	return pg_ls_dir_files(fcinfo, Log_directory, false);
 }
 
 /* Function to return the list of files in the WAL directory */
 Datum
 pg_ls_waldir(PG_FUNCTION_ARGS)
 {
-	return pg_ls_dir_files(fcinfo, XLOGDIR);
+	return pg_ls_dir_files(fcinfo, XLOGDIR, false);
+}
+
+/*
+ * Generic function to return the list of files in pgsql_tmp
+ */
+static Datum
+pg_ls_tmpdir(FunctionCallInfo fcinfo, Oid tblspc)
+{
+	char		path[MAXPGPATH];
+
+	if (!SearchSysCacheExists1(TABLESPACEOID, ObjectIdGetDatum(tblspc)))
+		ereport(ERROR,
+				(errcode(ERRCODE_UNDEFINED_OBJECT),
+				 errmsg("tablespace with OID %u does not exist",
+						tblspc)));
+
+	TempTablespacePath(path, tblspc);
+	return pg_ls_dir_files(fcinfo, path, true);
+}
+
+/*
+ * Function to return the list of temporary files in the pg_default tablespace's
+ * pgsql_tmp directory
+ */
+Datum
+pg_ls_tmpdir_noargs(PG_FUNCTION_ARGS)
+{
+	return pg_ls_tmpdir(fcinfo, DEFAULTTABLESPACE_OID);
+}
+
+/*
+ * Function to return the list of temporary files in the specified tablespace's
+ * pgsql_tmp directory
+ */
+Datum
+pg_ls_tmpdir_1arg(PG_FUNCTION_ARGS)
+{
+	return pg_ls_tmpdir(fcinfo, PG_GETARG_OID(0));
 }