[syslog-ng] file follow and new-file detection logic

[Evan Rempel]

syslog-ng 2.0.8

I am just starting to use the "file" source to follow files and
would like to make a suggestion as to how this mechanism should work.

Currently I understand that on startup, syslog-ng reads the persistent
data file to determine where is "left off" in a file and resumes from that location.
My concern is what it does if the file is no longer the same file.

It seems that in the case where the file has changed, that none of the existing
data in the file is processed by syslog-ng, and only new data arriving in the file
is processed.

I propose that the information saved in the persistent file should include
the offset within the file, and upon starting, if the offset does not match
a line break, then the file is no longer the same file and should be processed
from the beginning. Also, if the file is smaller than the offset, it is a new file
and should be processed from the beginning.

Evan Rempel.