2010-10-23 (í), 10:40 -0700, Andrew Morton: > On Sat, 23 Oct 2010 22:44:42 +0900 Namhyung Kim <namhyung@xxxxxxxxx> wrote: > > > Hello, > > > > I see block_prepare_write() has local variable wait[2] to keep track of > > buffer_heads which are not up-to-date. But I'm wondering how it could be > > guaranteed there will be no more than 2 such buffer_heads? Is there any > > restriction on the usage of the function? Using MAX_BUF_PER_PAGE instead > > of the magic number 2 is just useless? I couldn't find any comments or > > documentation on this. > > > > Any of your comments would be greatly appreciated. TIA. :-) > > > > block_prepare_write() may need to preread any buffer_head which are > being only partially modified by the write(). > > Buffers which aren't being modified at all don't need to be preread. > Buffers which are being fully modified don't need to be preread > (because all their data is being overwritten). > > page: |-----------------------| > buffer_heads: |-----|-----|-----|-----| > area we're writing to: |---------| > > There can only be a maximum of two partially-modified buffers in the page. I see. It considers both edges of the to-be-written data. Thanks for your clear and kindly explanation. :-) -- Regards, Namhyung Kim -- To unsubscribe from this list: send the line "unsubscribe linux-fsdevel" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
