Truncating the current log file while a reader is still reading through
it results in log lines getting missed. In contrast, rotating the file
allows readers who have the file open can continue to read from it
undisturbed. Rotating frees up the file name for the logger to create a
new file in its place. This remains true even when max-file=1; the
current log file is "rotated" from its name without giving it a new one.
On POSIXy filesystem APIs, rotating the last file is straightforward:
unlink()ing a file name immediately deletes the name from the filesystem
and makes it available for reuse, even if processes have the file open
at the time. Windows on the other hand only makes the name available
for reuse once the file itself is deleted, which only happens when no
processes have it open. To reuse the file name while the file is still
in use, the file needs to be renamed. So that's what we have to do:
rotate the file to a temporary name before marking it for deletion.
Signed-off-by: Cory Snider <csnider@mirantis.com>
This fixes the case where log rotation fails on Windows while there are
clients reading container logs.
Evicts readers if there is an error during rotation and try rotation again.
This is needed for Windows with this scenario:
1. `docker logs -f` is called
2. Log rotation occurs (log.txt -> log.txt.1, truncate and re-open
log.txt)
3. Log rotation occurs again (rm log.txt.1, log.txt -> log.txt.1)
On step 3, before this change, the log rotation will fail with `Access
is denied`.
In this case, what we have is a reader holding a file handle to the
primary log file. The log file is then rotated, but the reader still has
a the handle open. `FILE_SHARE_DELETE` allows this to happen... but then
we try to do it again for the next rotation and it blows up.
So when it blows up we force all the readers to disconnect, close the
log file, and try rotation again, which will succeed based on the added
tests.
Signed-off-by: Brian Goff <cpuguy83@gmail.com>
This makes sure, on Windows, that all files are opened with
FILE_SHARE_DELETE.
On non-Windows this just calls the same `os.Open()`.
Signed-off-by: Brian Goff <cpuguy83@gmail.com>
This fixes issues where one goroutine tries to delete or rename a file
while another goroutine has the file open (e.g. a log reader).
Signed-off-by: Brian Goff <cpuguy83@gmail.com>
Cory Snider