Add a trigger to force an ENOBUFS return from scoutfs_alloc_data()

Create the force-enobufs test and use the trigger to inject ENOBUFS
to test its handling in the direct and buffered write paths.

Signed-off-by: Chris Kirby <ckirby@versity.com>

kmod/src/alloc.c

@@ -744,6 +744,15 @@ int scoutfs_alloc_data(struct super_block *sb, struct scoutfs_alloc *alloc,
 	u64 len;
 	int ret;
 
+	/*
+	 * Force an ENOBUFS error below by pretending we got -ENOENT back from
+	 * the extent allocator.
+	 */
+	if (unlikely(scoutfs_trigger(sb, ALLOC_DATA_ENOBUFS))) {
+		ret = -ENOENT;
+		goto out;
+	}
+
 	/* large allocations come straight from the allocator */
 	if (count >= SCOUTFS_ALLOC_DATA_LG_THRESH) {
 		ret = scoutfs_ext_alloc(sb, &alloc_ext_ops, &args,

kmod/src/triggers.c

@@ -48,6 +48,7 @@ static char *names[] = {
 	[SCOUTFS_TRIGGER_RECLAIM_SKIP_FINALIZE] = "reclaim_skip_finalize",
 	[SCOUTFS_TRIGGER_LOG_MERGE_FORCE_PARTIAL] = "log_merge_force_partial",
 	[SCOUTFS_TRIGGER_ALLOC_FILL_FREED_LIST] = "alloc_fill_freed_list",
+	[SCOUTFS_TRIGGER_ALLOC_DATA_ENOBUFS] = "alloc_data_enobufs",
 };
 
 bool scoutfs_trigger_test_and_clear(struct super_block *sb, unsigned int t)

kmod/src/triggers.h

@@ -11,6 +11,7 @@ enum scoutfs_trigger {
 	SCOUTFS_TRIGGER_RECLAIM_SKIP_FINALIZE,
 	SCOUTFS_TRIGGER_LOG_MERGE_FORCE_PARTIAL,
 	SCOUTFS_TRIGGER_ALLOC_FILL_FREED_LIST,
+	SCOUTFS_TRIGGER_ALLOC_DATA_ENOBUFS,
 	SCOUTFS_TRIGGER_NR,
 };
 

tests/funcs/require.sh

@@ -38,3 +38,12 @@ t_require_meta_size() {
 	test "$dev_bytes" -ge "$req_bytes" || \
 		t_skip "$dev must be at least $req_iec, is $dev_iec"
 }
+
+#
+# Filter out direct I/O tests on platforms where we don't support it
+#
+t_require_o_direct() {
+	dd if=/dev/zero of="$T_D0/dio_test_file" count=0 oflag=direct status=none
+	test "$?" -eq "0" || \
+		t_skip_permitted "direct I/O not supported"
+}

tests/golden/force-enobufs

@@ -0,0 +1,7 @@
+== arm trigger
+== generate some direct I/O
+== confirm trigger fired
+== arm trigger
+== generate some buffered I/O
+== confirm trigger fired
+== cleanup

tests/sequence

@@ -12,6 +12,7 @@ simple-readdir.sh
 get-referring-entries.sh
 fallocate.sh
 basic-truncate.sh
+force-enobufs.sh
 punch-offline.sh
 data-prealloc.sh
 setattr_more.sh

tests/tests/force-enobufs.sh

@@ -0,0 +1,37 @@
+#
+# Use the ALLOC_DATA_ENOBUFS trigger to force an ENOBUFS return from
+# the data allocator.
+#
+
+t_require_commands dd rm
+t_require_o_direct
+
+echo "== arm trigger"
+t_trigger_arm_silent alloc_data_enobufs 0
+
+echo "== generate some direct I/O"
+dd if=/dev/zero of="$T_D0"/outfile_direct bs=65536 count=4096 oflag=direct status=none
+
+echo "== confirm trigger fired"
+if [ "$(t_trigger_get alloc_data_enobufs 0)" -ne "0" ]
+then
+	echo "trigger didn't fire for direct I/O"
+fi
+
+echo "== arm trigger"
+t_trigger_arm_silent alloc_data_enobufs 0
+
+echo "== generate some buffered I/O"
+dd if=/dev/zero of="$T_D0"/outfile_buffered bs=65536 count=1024 status=none
+
+echo "== confirm trigger fired"
+if [ "$(t_trigger_get alloc_data_enobufs 0)" -ne "0" ]
+then
+	echo "trigger didn't fire for buffered I/O"
+fi
+
+echo "== cleanup"
+rm -f "$T_D0"/outfile_direct
+rm -f "$T_D0"/outfile_buffered
+
+t_pass