stream: don't try to read from all-sparse/no-data files

[MoSal]

dd if=/dev/zero of=/tmp/10g.empty bs=1 seek=10G count=0
dd if=/dev/zero of=/tmp/10m.empty bs=1 seek=10M count=0
time mpv /tmp/10{g,m}.empty

I keep files with the name format ${name}-${hash}.${ext}.empty around, where the original is removed, and a sparse file with the size of the original is created instead.

A lot of time is wasted on such files when going through playlists/directories that include some of them.

This admittedly may not be that common of a use-case.

[github-actions]

Download the artifacts for this pull request:

Windows

• mpv-i686-w64-mingw32
• mpv-x86_64-w64-mingw32

macOS

• mpv-macos-14-arm
• mpv-macos-12-intel
• mpv-macos-13-intel

[MoSal]

Checks reveal support for SEEK_DATA is on for Linux, mac, and FreeBSD. And off for Windows and OpenBSD, as expected.

There is one exception. The check fails in linux-ffmpeg-4-4.

[na-na-hi]

There is one exception. The check fails in linux-ffmpeg-4-4.

SEEK_DATA was added for musl 1.2.3. Alpine Linux 3.15 (used for linux-ffmpeg-4-4) ships musl 1.2.2.

[MoSal]

There is one exception. The check fails in linux-ffmpeg-4-4.

SEEK_DATA was added for musl 1.2.3. Alpine Linux 3.15 (used for linux-ffmpeg-4-4) ships musl 1.2.2.

Cool. Thanks for the info.

[sfan5]

The use case is strange but I can't think of any downsides of rejecting empty files early like this, so should be fine.

[MoSal]

Review addressed.

[cheemeng]

@MoSal On MacOS Sonoma, this commit removes the ability to drag and drop a folder unto the mpv player.

[MoSal]

@cheemeng

Interesting. The seek doesn't fail with directories in GNU/Linux, even if they are empty.

Can you confirm this change fixes the issue?

 stream/stream_file.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/stream/stream_file.c b/stream/stream_file.c
index 0a6a697ff6..4b23d7fb83 100644
--- a/stream/stream_file.c
+++ b/stream/stream_file.c
@@ -359,7 +359,7 @@ static int open_f(stream_t *stream, const struct stream_open_args *args)
 #endif
 
 #if HAVE_SEEK_DATA
-    if (stream->mode == STREAM_READ) {
+    if (stream->mode == STREAM_READ && !stream->is_directory) {
         off_t first_data = lseek(p->fd, 0, SEEK_DATA);
         if (first_data == (off_t)-1 && errno == ENXIO) {
             MP_ERR(stream, "File is empty or all sparse (has no data).\n");

[sfan5]

@kasper93 and I discussed on IRC that we will likely be reverting this anyway because it also introduces an error message if you pass an empty file to e.g. --input-conf, which is nonsense.
The stream layer is just the wrong place to make this change.

[cheemeng]

Yup @MoSal , that would skip the throwing of errors when it's a directory, dragging in a folder works fine now.

PS: Perhaps this option to skip sparse files can also be added as one of the mpv list of 'features' in meson_options.txt so it can be disabled during compilation itself as well?

[MoSal]

@cheemeng
See comment above you in case you missed it.
Looks like this will be reverted altogether.