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There are two places where we look for unused CIDs: * First, while processing the list of existing contexts returned by CGDCONT?, we look for gaps in the used CIDs. E.g. if the first context has CID=1 and the next one has CID=3, we can definitely use the unused CID=2. * Then, while processing the response of CGDCONT=?, we try to see whether there is any empty CID available after the last existing one found. E.g. if the last existing context has CID=3 and the format tells us that the max allowed CID is 16, we can definitely use the unused CID=4. In both these cases, we should prefer using such an unused CID found to overwriting other CIDs that are already defined. This logic will now overwrite existing CIDs only if there are no unused CIDs, and the preference to overwrite is as follows: * If there is any existing context defined without an explicit APN, overwrite it. * Otherwise, overwrite the last existing CID found. * And in the worst case, when no list of contexts was loaded properly (e.g. some Android phones don't allow querying), fallback to overwriting CID=1.
ModemManager. ModemManager provides a unified high level API for communicating with mobile broadband modems, regardless of the protocol used to communicate with the actual device (Generic AT, vendor-specific AT, QCDM, QMI, MBIM...). Using. ModemManager is a system daemon and is not meant to be used directly from the command line. However, since it provides a DBus API, it is possible to use 'dbus-send' commands or the new 'mmcli' command line interface to control it from the terminal. The devices are queried from udev and automatically updated based on hardware events, although a manual re-scan can also be requested to look for RS232 modems. Implementation. ModemManager is a DBus system bus activated service (meaning it's started automatically when a request arrives). It is written in C, using glib and gio. Several GInterfaces specify different features that the modems support, including the generic MMIfaceModem3gpp and MMIfaceModemCdma which provide basic operations for 3GPP (GSM, UMTS, LTE) or CDMA (CDMA1x, EV-DO) modems. If a given feature is not available in the modem, the specific interface will not be exported in DBus. Plugins. Plugins are loaded on startup, and must implement the MMPlugin interface. It consists of a couple of methods which tell the daemon whether the plugin supports a port and to create custom MMBroadbandModem implementations. It most likely makes sense to derive custom modem implementations from one of the generic classes and just add (or override) operations which are not standard. There are multiple fully working plugins in the plugins/ directory that can be used as an example for writing new plugins. Writing new plugins is highly encouraged! The plugin API is open for changes, so if you're writing a plugin and need to add or change some public method, feel free to suggest it! License. The ModemManager and mmcli binaries are both GPLv2+. The libmm-glib library is LGPLv2+.