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FATFileSystem: provide working dir_rewind and dir_seek #5503

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merged 1 commit into from
Nov 20, 2017
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FATFileSystem: provide working dir_rewind and dir_seek #5503

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21 changes: 19 additions & 2 deletions features/filesystem/fat/FATFileSystem.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -660,7 +660,24 @@ void FATFileSystem::dir_seek(fs_dir_t dir, off_t offset) {
FATFS_DIR *dh = static_cast<FATFS_DIR*>(dir);

lock();
dh->index = offset;
if (offset < dh->index) {
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This optimisation assumes that index is monotonic increasing (which appears to be the case in the current version of ChaN FatFs). If not, rewind unconditionally and use an equality test in the while loop.

f_rewinddir(dh);
}
while (dh->index < offset) {
FILINFO finfo;
FRESULT res;
#if _USE_LFN
char lfname[NAME_MAX];
finfo.lfname = lfname;
finfo.lfsize = NAME_MAX;
#endif // _USE_LFN
res = f_readdir(dh, &finfo);
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Return value/error here will not be propagated to application.

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The only useful thing an application can do after dir_seek() is dir_read(), at which point it will receive an error.

if (res != FR_OK) {
break;
} else if (finfo.fname[0] == 0) {
break;
}
}
unlock();
}

Expand All @@ -678,7 +695,7 @@ void FATFileSystem::dir_rewind(fs_dir_t dir) {
FATFS_DIR *dh = static_cast<FATFS_DIR*>(dir);

lock();
dh->index = 0;
f_rewinddir(dh);
unlock();
}