logging: Add subsystem to log API (#19002)

Create new code paths for multiple subsystems in the code. This will
make maintaing this easier later.

Also introduce bugLogIf() for errors that should not happen in the first
place.

internal/hash/checksum.go

@@ -34,6 +34,10 @@ import (
 	"github.com/minio/minio/internal/logger"
 )
 
+func hashLogIf(ctx context.Context, err error) {
+	logger.LogIf(ctx, "hash", err)
+}
+
 // MinIOMultipartChecksum is as metadata on multipart uploads to indicate checksum type.
 const MinIOMultipartChecksum = "x-minio-multipart-checksum"
 
@@ -323,7 +327,7 @@ func (c *Checksum) AppendTo(b []byte, parts []byte) []byte {
 		var checksums int
 		// Ensure we don't divide by 0:
 		if c.Type.RawByteLen() == 0 || len(parts)%c.Type.RawByteLen() != 0 {
-			logger.LogIf(context.Background(), fmt.Errorf("internal error: Unexpected checksum length: %d, each checksum %d", len(parts), c.Type.RawByteLen()))
+			hashLogIf(context.Background(), fmt.Errorf("internal error: Unexpected checksum length: %d, each checksum %d", len(parts), c.Type.RawByteLen()))
 			checksums = 0
 			parts = nil
 		} else {