My concept with `class CancellableOperation` doesn't work properly,
because the kernel may continue to write to the given buffer as soon
as the read finishes.
To fix this, this commit adds `class ReadOperation` which owns the
buffer and the `struct iovec`. Instances of this class persist until
the read really finishes, even if the operation is canceled.
A bug report (https://github.com/MusicPlayerDaemon/MPD/issues/912)
suggests that on Linux, reading on `cifs` files may rarely return 0 (=
end of file) before the end of the file has really been reached. But
that's just a theory which I need to validate, so this runtime check
shall catch this condition before the assertion in
DecoderBridge::Read() crashes MPD. Let's see.
Closes https://github.com/MusicPlayerDaemon/MPD/issues/912
This is the final piece of the series to establish io_uring support on
Linux.
MPD doesn't need io_uring for its efficient bulk I/O support, but to
allow file I/O to be cancelled. This is a big problem on CIFS/NFS
mounts where processes sleep uninterruptable if the file server
disappears, deadlocking MPD.
With io_uring, a flaky NFS connection allows MPD to continue to work
(even though there are still deadlocks inside MPD which need to be
addressed).
This plugin does not yet use cancellable `open()` using
`IORING_OP_OPENAT`. This will be implemented later.
Lots of other optimization opportunities for io_uring are still
missing as well - for example the database update could benefit a lot,
but unfortunately, io_uring doesn't have `readdir()` support just yet.
The former is deprecated by C++14. The standard says they are the same:
The header defines all types and macros the same as the C standard library
header<stdint.h>.
Signed-off-by: Rosen Penev <rosenp@gmail.com>
The former was deprecated with C++14.
According to the C++11 and C++17 standards, both files are identical.
Signed-off-by: Rosen Penev <rosenp@gmail.com>
Version 10.2+0.93+1 was released five years ago in 2014 and is the
first version to feature cdio_cddap_free_messages(). There is no way
to check the libcdio-paranoia version at compile time, so let's just
remove support for older versions instead of attempting to fix the
cdio_cddap_free_messages() check at build time.
Closes https://github.com/MusicPlayerDaemon/MPD/issues/613
