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DataFlash: work around a NuttX bug 

the seek offset of files can get badly mucked up when it crosses
cluster boundaries. We need to fix this in NuttX, but meanwhile this
works around the bug. It seems that doing a lseek(fd, 0, SEEK_CUR)
fixes the seek offset in the file.

The bug seems to first happen at an offset of 315392. It also
doesn't happen every time - it is more likely to happen on the first
log download after booting
This commit is contained in:
Andrew Tridgell 2014-02-14 18:21:57 +11:00
parent 0aebc18b3f
commit 63910bf8cd
1 changed files with 19 additions and 0 deletions
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19
libraries/DataFlash/DataFlash_File.cpp
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@ -305,8 +305,26 @@ int16_t DataFlash_File::get_log_data(uint16_t log_num, uint16_t page, uint32_t o
_read_fd_log_num = log_num;
}
uint32_t ofs = page * (uint32_t)DATAFLASH_PAGE_SIZE + offset;
/*
this rather strange bit of code is here to work around a bug
in file offsets in NuttX. Every few hundred blocks of reads
(starting at around 350k into a file) NuttX will get the
wrong offset for sequential reads. The offset it gets is
typically 128k earlier than it should be. It turns out that
calling lseek() with 0 offset and SEEK_CUR works around the
bug. We can remove this once we find the real bug.
*/
if (ofs / 4096 != (ofs+len) / 4096) {
int seek_current = ::lseek(_read_fd, 0, SEEK_CUR);
if (seek_current != _read_offset) {
::lseek(_read_fd, _read_offset, SEEK_SET);
}
}
if (ofs != _read_offset) {
::lseek(_read_fd, ofs, SEEK_SET);
_read_offset = ofs;
}
int16_t ret = (int16_t)::read(_read_fd, data, len);
if (ret > 0) {
@ -426,6 +444,7 @@ void DataFlash_File::LogReadProcess(uint16_t log_num,
_read_offset = 0;
if (start_page != 0) {
::lseek(_read_fd, start_page * DATAFLASH_PAGE_SIZE, SEEK_SET);
_read_offset = start_page * DATAFLASH_PAGE_SIZE;
}
while (true) {