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@fritsch fritsch commented Jul 15, 2022

This tries to fix xbmc/xbmc#21603 by backporting the relevant upstream changes for the aviobuf allocation logic.

cus added 8 commits July 15, 2022 06:11
…the buffer

There was an off-by-one error when checking if the IO buffer still has enough
space till the end. One more byte can be safely written.

Signed-off-by: Marton Balint <cus@passwd.hu>
Existing code did not check if the requested seekback buffer is
already read entirely. In this case, nothing has to be done to guarantee
seekback.

Signed-off-by: Marton Balint <cus@passwd.hu>
The new buf_size was detemined too conservatively, maybe because of the
off-by-one issue which was fixed recently in fill_buffer. We can safely
substract 1 more from the new buffer size, because max_buffer_size space must
only be guaranteed when we are reading the last byte of the requested window.

Comparing the new buf_size against filled did not make a lot of sense, what
makes sense is that we want to reallocate the buffer if the new buf_size is
bigger than the old, therefore the change in the check.

Signed-off-by: Marton Balint <cus@passwd.hu>
…ck if needed

Previously ffio_ensure_seekback never flushed the buffer, so successive
ffio_ensure_seekback calls were all respected. This could eventually cause
unlimited memory and CPU usage if a demuxer called ffio_ensure_seekback on all
it's read data.

Most demuxers however only rely on being able to seek back till the position of
the last ffio_ensure_seekback call, therefore we change the semantics of
ffio_ensure_seekback so that a new call can invalidate seek guarantees of the
old. In order to support some level of "nested" ffio_ensure_seekback calls, we
document that the function only invalidates the old window (and potentially
discards the already read data from the IO buffer), if the newly requested
window does not fit into the old one.

This way we limit the memory usage for ffio_ensure_seekback calls requesting
consecutive data windows.

Signed-off-by: Marton Balint <cus@passwd.hu>
…k if not needed

Let's move unread data to the start of the old buffer instead.

Signed-off-by: Marton Balint <cus@passwd.hu>
Signed-off-by: Marton Balint <cus@passwd.hu>
…ize for streamed data

This should increase the effectiveness of ffio_ensure_seekback by reducing the
number of buffer reallocations and memmoves/memcpys because even a small
seekback window requires max_buffer_size+window_size buffer space.

Signed-off-by: Marton Balint <cus@passwd.hu>
…ead_partial"

This is unneeded after 2ca48e4 and it breaks
ffio_ensure_seekback().

This reverts commit 53c25ee.

Signed-off-by: Marton Balint <cus@passwd.hu>
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2 participants