使用 direct_io FUSE fseek 意外行为
我正在尝试编写一个 FUSE 文件系统，将流音乐呈现为 mp3 文件。我不想在仅读取 ID3v1.1 标签时开始流式传输音频，因此我使用 direct_io 和 max_readahead=0 挂载文件系统。
但是当我这样做时（这也是 libid3tag 所做的），我读取了 2752 个字节，距末尾偏移量为 -2880 个字节：
char tmp[255];
FILE* f = fopen("foo.mp3", "r");
fseek(f, -128, SEEK_END);
fread(tmp, 1, 10, f);
这是为什么？我希望得到一个读取调用，其偏移量距末尾正好 128 个字节，大小为 10。
读取的字节量似乎有所不同。
I'm trying to write a FUSE filesystem that presents streamable music as mp3 files. I don't want to start to stream the audio when just the ID3v1.1 tag is read, so I mount the filesystem with direct_io and max_readahead=0.
But when I do this (which is also what libid3tag does), I get reads of 2752 bytes with offset -2880 bytes from the end:
char tmp[255];
FILE* f = fopen("foo.mp3", "r");
fseek(f, -128, SEEK_END);
fread(tmp, 1, 10, f);
Why is this? I expect to get a call to read with an offset exactly 128 bytes from the end with size 10..
The amount of bytes read seems to vary somewhat.
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我也遇到过类似的问题，并向 s3fs 提交了问题。结账问题：http://code.google.com/p/s3fs/issues/detail?can=2&q=&colspec=ID%20Type% 20Status%20Priority%20Milestone%20Owner%20Summary&groupby=&sort=&id=241
另外，检查 s3fs.cpp 中的第 1611 行：
http://code.google.com/p/s3fs/source/browse/trunk/src/s3fs .cpp?r=316
I've had similar issue and filed an issue with s3fs. Checkout issue : http://code.google.com/p/s3fs/issues/detail?can=2&q=&colspec=ID%20Type%20Status%20Priority%20Milestone%20Owner%20Summary&groupby=&sort=&id=241
additionally, checkout line 1611 in the s3fs.cpp:
http://code.google.com/p/s3fs/source/browse/trunk/src/s3fs.cpp?r=316