eda47170ed
Our own implementation of a string buffer like GString.
Advantages (in decreasing relevance):
- Since we are in control, we can easily let it nm_explicit_bzero()
the memory. The regular GString API cannot be used in such a case.
While nm_explicit_bzero() may or may not be of questionable benefit,
the problem is that if the underlying API counteracts the aim of
clearing memory, it gets impossible. As API like NMStrBuf supports
it, clearing memory is a easy as enable the right flag.
This would for example be useful for example when we read passwords
from a file or file descriptor (e.g. try_spawn_vpn_auth_helper()).
- We have API like
nmp_object_to_string (const NMPObject *obj,
NMPObjectToStringMode to_string_mode,
char *buf,
gsize buf_size);
which accept a fixed size output buffer. This has the problem of
how choosing the right sized buffer. With NMStrBuf such API could
be instead
nmp_object_to_string (const NMPObject *obj,
NMPObjectToStringMode to_string_mode,
NMStrBuf *buf);
which can automatically grow (using heap allocation). It would be
easy to extend NMStrBuf to use a fixed buffer or limiting the
maximum string length. The point is, that the to-string API wouldn't
have to change. Depending on the NMStrBuf passed in, you can fill
an unbounded heap allocated string, a heap allocated string up to
a fixed length, or a static string of fixed length. NMStrBuf currently
only implements the unbounded heap allocate string case, but it would
be simple to extend.
Note that we already have API like nm_utils_strbuf_*() to fill a buffer
of fixed size. GString is not useable for that (efficiently), hence
this API exists. NMStrBuf could be easily extended to replace this API
without usability or performance penalty. So, while this adds one new
API, it could replace other APIs.
- GString always requires a heap allocation for the container. In by far
most of the cases where we use GString, we use it to simply construct
a string dynamically. There is zero use for this overhead. If one
really needs a heap allocated buffer, NMStrBuf can easily embedded
in a malloc'ed memory and boxed that way.
- GString API supports inserting and removing range. We almost never
make use of that. We only require append-only, which is simple to
implement.
- GString needs to NUL terminate the buffer on every append. It
has unnecessary overhead for allowing a usage of where intermediate
buffer contents are valid strings too. That is not the case with
NMStrBuf: the API requires the user to call nm_str_buf_get_str() or
nm_str_buf_finalize(). In most cases, you would only access the string
once at the end, and not while constructing it.
- GString always grows the buffer size by doubling it. I don't think
that is optimal. I don't think there is one optimal approach for how
to grow the buffer, it depends on the usage patterns. However, trying
to make an optimal choice here makes a difference. QT also thinks so,
and I adopted their approach in nm_utils_get_next_realloc_size().
****************** NetworkManager core daemon has moved to gitlab.freedesktop.org! git clone https://gitlab.freedesktop.org/NetworkManager/NetworkManager.git ****************** Networking that Just Works -------------------------- NetworkManager attempts to keep an active network connection available at all times. The point of NetworkManager is to make networking configuration and setup as painless and automatic as possible. NetworkManager is intended to replace default route, replace other routes, set IP addresses, and in general configure networking as NM sees fit (with the possibility of manual override as necessary). In effect, the goal of NetworkManager is to make networking Just Work with a minimum of user hassle, but still allow customization and a high level of manual network control. If you have special needs, we'd like to hear about them, but understand that NetworkManager is not intended for every use-case. NetworkManager will attempt to keep every network device in the system up and active, as long as the device is available for use (has a cable plugged in, the killswitch isn't turned on, etc). Network connections can be set to 'autoconnect', meaning that NetworkManager will make that connection active whenever it and the hardware is available. "Settings services" store lists of user- or administrator-defined "connections", which contain all the settings and parameters required to connect to a specific network. NetworkManager will _never_ activate a connection that is not in this list, or that the user has not directed NetworkManager to connect to. How it works: The NetworkManager daemon runs as a privileged service (since it must access and control hardware), but provides a D-Bus interface on the system bus to allow for fine-grained control of networking. NetworkManager does not store connections or settings, it is only the mechanism by which those connections are selected and activated. To store pre-defined network connections, two separate services, the "system settings service" and the "user settings service" store connection information and provide these to NetworkManager, also via D-Bus. Each settings service can determine how and where it persistently stores the connection information; for example, the GNOME applet stores its configuration in GConf, and the system settings service stores its config in distro-specific formats, or in a distro- agnostic format, depending on user/administrator preference. A variety of other system services are used by NetworkManager to provide network functionality: wpa_supplicant for wireless connections and 802.1x wired connections, pppd for PPP and mobile broadband connections, DHCP clients for dynamic IP addressing, dnsmasq for proxy nameserver and DHCP server functionality for internet connection sharing, and avahi-autoipd for IPv4 link-local addresses. Most communication with these daemons occurs, again, via D-Bus. Why doesn't my network Just Work? Driver problems are the #1 cause of why NetworkManager sometimes fails to connect to wireless networks. Often, the driver simply doesn't behave in a consistent manner, or is just plain buggy. NetworkManager supports _only_ those drivers that are shipped with the upstream Linux kernel, because only those drivers can be easily fixed and debugged. ndiswrapper, vendor binary drivers, or other out-of-tree drivers may or may not work well with NetworkManager, precisely because they have not been vetted and improved by the open-source community, and because problems in these drivers usually cannot be fixed. Sometimes, command-line tools like 'iwconfig' will work, but NetworkManager will fail. This is again often due to buggy drivers, because these drivers simply aren't expecting the dynamic requests that NetworkManager and wpa_supplicant make. Driver bugs should be filed in the bug tracker of the distribution being run, since often distributions customize their kernel and drivers. Sometimes, it really is NetworkManager's fault. If you think that's the case, please file a bug at: https://gitlab.freedesktop.org/NetworkManager/NetworkManager/issues Attaching NetworkManager debug logs from the journal (or wherever your distribution directs syslog's 'daemon' facility output, as /var/log/messages or /var/log/daemon.log) is often very helpful, and (if you can get) a working wpa_supplicant config file helps enormously. See the logging section of file contrib/fedora/rpm/NetworkManager.conf for how to enable debug logging in NetworkManager.