http://mail.gnu.org/archive/html/bug-textutils/2003-05/msg00007.html
(file_lines): Add new parameter, *read_pos, and set it.
(pipe_lines, pipe_bytes, start_bytes, start_lines): Likewise.
(tail_bytes, tail_lines, tail): Likewise.
(tail_file): Use the new `read_pos' value as the size,
rather than stats.st_size from the fstat call.
Use quote in diagnostics. Change many error format strings
from just `%s' to e.g., `error reading %s'.
(pipe_lines): Change type of parameter, n_lines, to uintmax_t.
Rewrite newline-counting loop to use memchr.
(dump_remainder): Move two declarations `down' into the scope
where they are used.
(xlseek): Return the resulting offset.
(file_lines): Rename parameter, file_length, to end_pos.
(pipe_lines): Don't coerce safe_read return value to `int'.
Adapt tests accordingly.
(pipe_bytes) [struct charbuffer] (nbytes): Change type from `int'
to `unsigned int'.
Change type of `total_bytes' from `int' to `size_t',
since the former wouldn't always be wide enough.
Don't coerce safe_read return value to `int',
and adapt tests accordingly.
Now that testing for a read error no longer involves
using `tmp', handle that case *after* freeing `tmp'.
(start_bytes): Clean up.
(tail_bytes): Now that `n_bytes' may be larger than
OFF_T_MAX, test for that condition and, if it's true, don't
use lseek optimizations.
(parse_options): Don't fail just because N_UNITS is larger than
the maximum size of a file -- tail may be applied to an input
stream (e.g., a pipe) with more data than that.
[this change is analogous (bytes vs. lines) to the one of 2002-01-27]
(start_bytes): Detect EOF, inform caller.
(tail_bytes): Upon EOF in start_bytes, return immediately.
(file_lines): Reorganize to use memrchr rather than an explicit loop.
Adapt to new safe_read ABI.
Move declaration of global variable, sleep_interval, to ...
(main): ...here.
(usage): Update description of --sleep-interval option.
(tail_forever): New parameter, sleep_interval. Update caller.
Use xnanosleep, rather than sleep.
(parse_options): New parameter, sleep_interval. Update caller.
Use xstrtod, now that we accept floating point values.
max_n_unchanged_stats_between_opens specially (as if it were
infinite) if it has its maximal value. Similarly for
max_n_consecutive_size_changes_between_opens.
(usage): Document only the intersection of the old and new behaviors,
to encourage portability.
(main, parse_obsolescent_option): Parse options using POSIX 1003.1-2001 rules if
conforming to that standard. Do not warn of obsolete options.
support of obsolete "-N" option syntax in expand, head, fold,
split, tail, unexpand, uniq, and which prohibits options with
optional arguments in od and pr.
(parse_obsolescent_option, main): Likewise.
Split usage strings so that --help and --version descriptions are alone
in their own string.
Likewise for the one that says:
Mandatory arguments to long options are mandatory for short options too.
Work properly even when the read pointer is not at beginning of file.
(tail_lines): Call file_lines for any regular file, as long as lseek
can be used to seek to its end, not just when the initial read pointer
is at beginning of file.
Jim Meyering