Fix volume allocation with max=0 and minFreeSpace - prevent allocate-then-delete behavior (#7147)

* Initial plan

* Fix volume allocation with max=0 and minFreeSpace - prevent allocate-then-delete behavior

Co-authored-by: chrislusf <1543151+chrislusf@users.noreply.github.com>

* improve tests

* table driven

* Update weed/storage/store.go

Co-authored-by: gemini-code-assist[bot] <176961590+gemini-code-assist[bot]@users.noreply.github.com>

* add tests

* add more tests

---------

Co-authored-by: copilot-swe-agent[bot] <198982749+Copilot@users.noreply.github.com>
Co-authored-by: chrislusf <1543151+chrislusf@users.noreply.github.com>
Co-authored-by: chrislu <chris.lu@gmail.com>
Co-authored-by: Chris Lu <chrislusf@users.noreply.github.com>
Co-authored-by: gemini-code-assist[bot] <176961590+gemini-code-assist[bot]@users.noreply.github.com>

1 files changed, 94 insertions, 0 deletions

diff --git a/weed/storage/store_disk_space_test.go b/weed/storage/store_disk_space_test.go
new file mode 100644
index 000000000..284657e3c
--- /dev/null
+++ b/weed/storage/store_disk_space_test.go
@@ -0,0 +1,94 @@
+package storage
+
+import (
+	"testing"
+
+	"github.com/seaweedfs/seaweedfs/weed/storage/needle"
+)
+
+func TestHasFreeDiskLocation(t *testing.T) {
+	testCases := []struct {
+		name           string
+		isDiskSpaceLow bool
+		maxVolumeCount int32
+		currentVolumes int
+		expected       bool
+	}{
+		{
+			name:           "low disk space prevents allocation",
+			isDiskSpaceLow: true,
+			maxVolumeCount: 10,
+			currentVolumes: 5,
+			expected:       false,
+		},
+		{
+			name:           "normal disk space and available volume count allows allocation",
+			isDiskSpaceLow: false,
+			maxVolumeCount: 10,
+			currentVolumes: 5,
+			expected:       true,
+		},
+		{
+			name:           "volume count at max prevents allocation",
+			isDiskSpaceLow: false,
+			maxVolumeCount: 2,
+			currentVolumes: 2,
+			expected:       false,
+		},
+		{
+			name:           "volume count over max prevents allocation",
+			isDiskSpaceLow: false,
+			maxVolumeCount: 2,
+			currentVolumes: 3,
+			expected:       false,
+		},
+		{
+			name:           "volume count just under max allows allocation",
+			isDiskSpaceLow: false,
+			maxVolumeCount: 2,
+			currentVolumes: 1,
+			expected:       true,
+		},
+		{
+			name:           "max volume count is 0 allows allocation",
+			isDiskSpaceLow: false,
+			maxVolumeCount: 0,
+			currentVolumes: 100,
+			expected:       true,
+		},
+		{
+			name:           "max volume count is 0 but low disk space prevents allocation",
+			isDiskSpaceLow: true,
+			maxVolumeCount: 0,
+			currentVolumes: 100,
+			expected:       false,
+		},
+	}
+
+	for _, tc := range testCases {
+		t.Run(tc.name, func(t *testing.T) {
+			// setup
+			diskLocation := &DiskLocation{
+				volumes:        make(map[needle.VolumeId]*Volume),
+				isDiskSpaceLow: tc.isDiskSpaceLow,
+				MaxVolumeCount: tc.maxVolumeCount,
+			}
+			for i := 0; i < tc.currentVolumes; i++ {
+				diskLocation.volumes[needle.VolumeId(i+1)] = &Volume{}
+			}
+
+			store := &Store{
+				Locations: []*DiskLocation{diskLocation},
+			}
+
+			// act
+			result := store.hasFreeDiskLocation(diskLocation)
+
+			// assert
+			if result != tc.expected {
+				t.Errorf("Expected hasFreeDiskLocation() = %v; want %v for volumes:%d/%d, lowSpace:%v",
+					result, tc.expected, len(diskLocation.volumes), diskLocation.MaxVolumeCount, diskLocation.isDiskSpaceLow)
+			}
+		})
+	}
+}