[FFmpeg-trac] #9940(undetermined:new): sendcmd Error occurred in mmap()

FFmpeg trac at avcodec.org
Fri Sep 23 16:21:34 EEST 2022

#9940: sendcmd Error occurred in mmap()
             Reporter:  Jozef        |                     Type:  defect
  Chutka                             |
               Status:  new          |                 Priority:  normal
            Component:               |                  Version:
  undetermined                       |  unspecified
             Keywords:               |               Blocked By:
             Blocking:               |  Reproduced by developer:  0
Analyzed by developer:  0            |
 Using the latest ffmpeg compiled with emscripten, I am not able to resolve
 `[Parsed_sendcmd_6 @ 0x280af40] [FILE @ 0x17f3690] Error occurred in
 mmap(): No such device` error when using `sendcmd=f=/mydir/myfile.txt`.

 I have a readonly FS mounted as `/mydir` but for some reason ffmpeg can
 not resolve `/mydir/myfile.txt` which surely does exist.

 Interestingly I can use `movie=/mydir/myinput.mp4` to load input from the
 same FS.

 I tried to understand what is the difference between reading a file from
 `sendcmd` vs. `movie` and it seems the first is using `mmap()` (inside
 av_file_map()) while the other `io_open()` (inside AVFormatContext, sorry
 not able to locate deeper) and reads it as an IO Stream... (?)

 Reading file.c, I can see some other opening procedures based on HAVE_MMAP
 / HAVE_MAPVIEWOFFILE, but I am not sure how or if this can be available
 with emscripten build.

 I wonder if this is something that can be resolved on my side or something
 ffmpeg team can take a look into?
Ticket URL: <https://trac.ffmpeg.org/ticket/9940>
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