implement logging redirection

Author: ogad-tether

tools/mtmd/README.md

@@ -37,6 +37,37 @@ Built upon `clip.cpp` (similar to `llava.cpp`), `libmtmd` offers several advanta
 - **Improved UX/DX:** Features a more intuitive API, inspired by the `Processor` class in the Hugging Face `transformers` library.
 - **Flexibility:** Designed to support multiple input types (text, audio, images) while respecting the wide variety of chat templates used by different models.
 
+## Logging Configuration
+
+By default, `libmtmd` logs messages directly to stderr. To integrate `libmtmd` logging with your application's logging system, you can use the `mtmd_log_set_llama_callback()` function to redirect all mtmd/clip logs through llama's logging callback.
+
+**Example usage:**
+
+```c
+#include "llama.h"
+#include "mtmd.h"
+
+// Your custom logging callback
+void my_log_callback(ggml_log_level level, const char * text, void * user_data) {
+    // Your logging logic here
+    printf("[%d] %s", level, text);
+}
+
+int main() {
+    // Set up llama's logging
+    llama_log_set(my_log_callback, NULL);
+    
+    // Redirect mtmd/clip logging to use the same callback
+    mtmd_log_set_llama_callback(my_log_callback, NULL);
+    
+    // Now all mtmd and clip logs will use your custom callback
+    mtmd_context * ctx = mtmd_init_from_file(...);
+    // ...
+}
+```
+
+This ensures that all logging from `libmtmd`, including the underlying `clip.cpp` vision encoder, is routed through your application's logging system consistently.
+
 ## How to obtain `mmproj`
 
 Multimodal projector (`mmproj`) files are specific to each model architecture.

tools/mtmd/clip-impl.h

@@ -203,10 +203,33 @@ struct clip_logger_state {
     ggml_log_level verbosity_thold;
     ggml_log_callback log_callback;
     void * log_callback_user_data;
+    // Store the llama callback to forward logs to
+    ggml_log_callback llama_callback;
+    void * llama_callback_user_data;
 };
 
 extern struct clip_logger_state g_logger_state;
 
+// Callback that redirects to llama's logging system
+static void clip_log_callback_llama(enum ggml_log_level level, const char * text, void * user_data) {
+    (void) user_data;
+    // Forward to the stored llama callback if available
+    if (g_logger_state.llama_callback != nullptr) {
+        g_logger_state.llama_callback(level, text, g_logger_state.llama_callback_user_data);
+    } else {
+        // Fallback to default if no llama callback is set
+        clip_log_callback_default(level, text, user_data);
+    }
+}
+
+// Function to enable llama logging redirection
+// This should be called after llama_log_set has been called to set up llama's logging
+static inline void clip_log_use_llama_callback(ggml_log_callback llama_cb, void * llama_user_data) {
+    g_logger_state.llama_callback = llama_cb;
+    g_logger_state.llama_callback_user_data = llama_user_data;
+    g_logger_state.log_callback = clip_log_callback_llama;
+}
+
 static void clip_log_internal_v(enum ggml_log_level level, const char * format, va_list args) {
     if (format == NULL) {
         return;

tools/mtmd/clip.cpp

@@ -28,7 +28,13 @@
 #include <numeric>
 #include <functional>
 
-struct clip_logger_state g_logger_state = {GGML_LOG_LEVEL_CONT, clip_log_callback_default, NULL};
+struct clip_logger_state g_logger_state = {
+    GGML_LOG_LEVEL_CONT,           // verbosity_thold
+    clip_log_callback_default,     // log_callback
+    NULL,                          // log_callback_user_data
+    nullptr,                       // llama_callback
+    nullptr                        // llama_callback_user_data
+};
 
 enum ffn_op_type {
     FFN_GELU,

tools/mtmd/mtmd.cpp

@@ -363,6 +363,10 @@ void mtmd_free(mtmd_context * ctx) {
     }
 }
 
+void mtmd_log_set_llama_callback(ggml_log_callback llama_cb, void * llama_user_data) {
+    clip_log_use_llama_callback(llama_cb, llama_user_data);
+}
+
 struct mtmd_tokenizer {
     mtmd_context * ctx;
     std::vector<const mtmd_bitmap *> bitmaps;

tools/mtmd/mtmd.h

@@ -96,6 +96,14 @@ MTMD_API mtmd_context * mtmd_init_from_file(const char * mmproj_fname,
 
 MTMD_API void mtmd_free(mtmd_context * ctx);
 
+// Set up logging to use llama's logging callback
+// This redirects all mtmd/clip logging through llama's logging system
+// Call this after llama_log_set to ensure mtmd uses the same logging callback
+// Example:
+//   llama_log_set(my_log_callback, my_user_data);
+//   mtmd_log_set_llama_callback(my_log_callback, my_user_data);
+MTMD_API void mtmd_log_set_llama_callback(ggml_log_callback llama_cb, void * llama_user_data);
+
 // whether we need to set non-causal mask before llama_decode
 MTMD_API bool mtmd_decode_use_non_causal(mtmd_context * ctx);