I can kinda see the bind something like ext4 is in, since the change smacks a little of a "flag day" for "how ext4 prints messages from the kernel". Any bugfix or stability patch made to ext4 after the printk->pr_XXX change will be that much harder to backport those changes to a kernel that existed before that "flag day".
That said, once the pr_XXX functions have been in release kernels long enough that the oldest relevant 'stable' release has them (what's that, about a year? year and a half?), then it seems like you can incrementally start folding the pr_XXX changes in, file by file. Then a backport will convert some fraction of printk calls relatively painlessly, it seems. Either that, or you could execute a much less exciting 'flag day' patch on ext4 to convert printk to the newer forms, and make it a prereq for any further bugfixes/improvements. Because all the relevant back-port targets will have pr_XXX, at least it'll be mostly painless.
Right now, though, am I wrong in thinking that the printk->pr_XXX changes make it just that bit more difficult to migrate patches to older, pre-change kernels, as long as the patch overlaps one of these conversions?
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