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# udebug - OpenWrt debugging infrastructure
udebug assists whole-system debugging by making it easy to provide ring buffers
with debug data and make them accessible through a unified API.
Through the CLI, you can either create snapshots of data with a specific duration,
or stream data in real time. The data itself is stored in .pcapng files, which can
contain a mix of packets and log messages.
## Notes on using Wireshark
In order to parse log messages in .pcapng files, you need to change the Wireshark
configuration.
Under `Preferences` -> `Protocols` -> `DLT_USER` -> `Encapsulations Table`,
add an entry for `User 0 (DLT=147)` with Payload protocol `syslog`.
## libudebug C API
#### `void udebug_init(struct udebug *ctx)`
Initializes the udebug context. Must be called before adding buffers.
#### `int udebug_connect(struct udebug *ctx, const char *path)`
Connect to udebugd and submit any buffers that were added using `udebug_buf_add`.
#### `void udebug_auto_connect(struct udebug *ctx, const char *path)`
Connects and automatically reconnects to udebugd. Uses uloop and calls `udebug_add_uloop`.
#### `void udebug_free(struct udebug *ctx)`
Frees the udebug context and all added created buffers.
#### `int udebug_buf_init(struct udebug_buf *buf, size_t entries, size_t size)`
Allocates a buffer with a given size. Entries and size are rounded up internally to the
nearest power-of-2.
#### `int udebug_buf_add(struct udebug *ctx, struct udebug_buf *buf, const struct udebug_buf_meta *meta);`
Submits the buffer to udebugd and makes it visible.
#### `void udebug_buf_free(struct udebug_buf *buf)`
Removes the buffer from udebugd and frees it.
#### `void udebug_entry_init(struct udebug_buf *buf)`
Initializes a new entry on the ring buffer.
#### `void *udebug_entry_append(struct udebug_buf *buf, const void *data, uint32_t len)`
Appends data to the ring buffer. When called with data == NULL, space is only
reserved, and the return value provides a pointer with len bytes that can be
written to.
#### `int udebug_entry_printf(struct udebug_buf *buf, const char *fmt, ...)`
Appends a string to the buffer, based on format string + arguments (like printf)
#### `int udebug_entry_vprintf(struct udebug_buf *buf, const char *fmt, va_list ap)`
Like `udebug_entry_printf()`
#### `void udebug_entry_add(struct udebug_buf *buf)`
Finalizes and publishes the entry on the ring buffer.
### Simple example
```
static struct udebug ud;
static struct udebug_buf udb;
/* ... */
uloop_init();
udebug_init(&ud);
udebug_auto_connect(&ud, NULL);
static const struct udebug_buf_meta buf_meta = {
.name = "counter",
.format = UDEBUG_FORMAT_STRING,
};
int entries = 128;
int data_size = 1024;
udebug_buf_init(&udb, entries, data_size);
udebug_buf_add(&ud, &udb, &buf_meta);
/* ... */
udebug_entry_init(&udb); // initialize entry
udebug_entry_printf(&udb, "count=%d", count++);
udebug_entry_add(&udb); // finalize the entry
```
## udebug CLI
```
Usage: udebug-cli [<options>] <command> [<args>]
Options:
-f Ignore errors on opening rings
-d <duration>: Only fetch data up to <duration> seconds old
-o <file>|- Set output file for snapshot/stream (or '-' for stdout)
-i <process>[:<name>] Select debug buffer for snapshot/stream
-s <path> Use udebug socket <path>
-q Suppress warnings/error messages
Commands:
list: List available debug buffers
snapshot: Create a pcapng snapshot of debug buffers
set_flag [<name>=0|1 ...] Set ring buffer flags
get_flags Get ring buffer flags
```
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