Lufs does not log user data updates to a file. If you have a 512 byte
file and change the contents of this file, lufs will not log this.
However if you are extending this file lufs will track the additional
blocks allocated to the file. If the system crashes before the log map
is updated to track these changes, the file will look as if nothing has
changed, i.e. no additional blocks will be allocated to the file, and
the blocks that were allocated, will be seen still as free.
Yuen L. Lee wrote:
I'm interested in how lufs handles a data block update request. Here is my
question: Suppose, a small file is opened, its 512 bytes is modified. I'm
wondering how lufs
works, does it ask the seg_map driver to map in the 512 bytes of the file we
are going to replace once the modified data is copied to the kernel space from
the user space then perform ufs_pustpage()? If so, what will the newly updated
data fragment look like if the system crashes during the metadata update from
in-core delta map to log_map. After the system is re-booted, do I get the
newly modified data or does the un-modified data remain? Many thanks in
advance.
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