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Re: Major JFFS2 bug (?)
> The mv should be atomic on JFFS2. It would be useful for someone to
> build a test script to insure that this is the case. Ie: after a power
> cycle you either have all of foo.new in foo or the old foo. There
> should never be a mix according to dwmw2's comments as to how this is
To clarify - there are three operations to do, all three of which should
happen in a single transaction upon 'mv foo.new foo':
- Remove old dirent 'foo' if it existed, i_nlink--;
- Create new dirent 'foo' pointing to the old 'foo.new' inode.
- Remove old dirent 'foo.new'
JFFS2 currently does the first two atomically in a single transaction, then
attempts the third.
So you'll always end up with either _all_ of the original 'foo' or _all_ of
'foo.new' in what's now known as 'foo'. They're entirely different inodes,
and all that rename() changes is directory entries. If the final operation
goes wrong, you might actually end up with a hard link though.
In fact, jffs2_rename() will attempt to remove the newly-created 'foo'
dirent if the third operation (removing 'foo.new') fails, to prevent the
creation of a hard link. In the case where an old 'foo' didn't exist, that
makes sense. In the case where and old 'foo' _did_ exist, however, that is
entirely the wrong thing to do, and will leave _no_ dirent for 'foo' on the
medium. I'll fix that.
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