Hi! > On filesystems where blocksize < pagesize the situation is more complicated. > Think for example that blocksize = 1024, pagesize = 4096 and a process does: > ftruncate(fd, 0); > pwrite(fd, buf, 1024, 0); > map = mmap(NULL, 4096, PROT_WRITE, MAP_SHARED, fd, 0); > map[0] = 'a'; ----> page_mkwrite() for index 0 is called > ftruncate(fd, 10000); /* or even pwrite(fd, buf, 1, 10000) */ > fsync(fd); ----> writepage() for index 0 is called > > At the moment page_mkwrite() is called, filesystem can allocate only one block > for the page because i_size == 1024. Otherwise it would create blocks beyond > i_size which is generally undesirable. But later at writepage() time, we would > like to have blocks allocated for the whole page (and in principle we have to > allocate them because user could have filled the page with data after the > second ftruncate()). This patch introduces a framework which allows filesystems > to handle this with a reasonable effort. What happens when you do above sequence on today's kernels? Oops? 3000 bytes of random junk in file? ...? -- (english) http://www.livejournal.com/~pavelmachek (cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html -- To unsubscribe from this list: send the line "unsubscribe linux-ext4" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
