Because the utmpx interface is generally not required to be thread-safe,
but it is nice to have, if easy to do so. Therefore don't make a mess
out of the code and only use it if __NO_TLS is not defined.
If the utmpx database gets updated while an application is reading it,
there is a chance the reading application processes partially
overwritten entries. To solve this, make sure we always read a multiple
of sizeof(struct futx) at a time.
MFC after: 2 weeks
- Massively reduce BSS usage. Let futx_to_utx() dynamically allocate the
structure. There is only a very small amount of applications out there
that needs to use the utmpx database. Wasting 1 KB on unused
structures makes little sense.
- Just let getutxid() search for matching ut_id's for any *PROCESS-type.
This makes the code a bit more future-proof.
- Fix a POSIX-mistake: when reading POSIX and the OpenSolaris
implementation, getutxline() must return USER_PROCESS and
LOGIN_PROCESS records whose ut_lines match. When reading POSIX, it
seems LOGIN_PROCESS should not use ut_line at the first place. I have
reported this issue.
The utmpx interface is the standardized interface of the user accounting
database. The standard only defines a subset of the functions that were
present in System V-like systems.
I'd like to highlight some of the traits my implementation has:
- The standard allows the on-disk format to be different than the
in-memory representation (struct utmpx). Most operating systems don't
do this, but we do. This allows us to keep our ABI more stable, while
giving us the opportunity to modify the on-disk format. It also allows
us to use a common file format across different architectures (i.e.
byte ordering).
- Our implementation of pututxline() also updates wtmp and lastlog (now
called utx.log and utx.lastlogin). This means the databases are more
likely to be in sync.
- Care must be taken that our implementation discard any fields that are
not applicable. For example, our DEAD_PROCESS records do not hold a
TTY name. Just a time stamp, a record identifier and a process
identifier. It also guarantees that strings (ut_host, ut_line and
ut_user) are null terminated. ut_id is obviously not null terminated,
because it's not a string.
- The API and its behaviour should be conformant to POSIX, but there may
be things that slightly deviate from the standard. This implementation
uses separate file descriptors when writing to the log files. It also
doesn't use getutxid() to search for a field to overwrite. It uses an
allocation strategy similar to getutxid(), but prevents DEAD_PROCESS
records from accumulating.
Make sure libulog doesn't overwrite the manpages shipped with our C
library. Also keep the symbol list in Symbol.map sorted.
I'll bump __FreeBSD_version later this evening. I first want to convert
everything to <utmpx.h> and get rid of <utmp.h>.
