On Thu, Jul 22, 2021 at 09:17:54AM -0700, Eric Biggers wrote: > > I think it matches with FIEMAP_EXTENT_UNWRITTEN. Otherwise, we should > > shorten the last extent like below. > > > > fe_logical=0 fe_physical=16384 length=4096 > > fe_logical=4096 fe_physical=81920 length=4096 > > fe_logical=8192 fe_physical=147456 length=4096 > > > > > > Unwritten extent - the extent is allocated but its data has not been > > initialized. This indicates the extent's data will be all zero if read > > through the filesystem but the contents are undefined if read directly > > from > > the device. > > Well, as I said before, using UNWRITTEN isn't appropriate because it indicates > that the data is all zeroes, which in this case it is not. Similarly, > reporting > a hole isn't appropriate because it also indicates that the data is all zeroes > and also that it has no space allocated on-disk at all. > > I think we should just over-report the physical length of the last extent in > the > cluster, which is what btrfs does... >
Also keep in mind that as far as fiemap is concerned, when FIEMAP_EXTENT_ENCODED is set (indicating that the data is compressed or encrypted), then reading the data from disk will have "undefined results"; see Documentation/filesystems/fiemap.rst. As such, when someone decides to do so anyway (which is necessary for encryption testing), they really need to know *exactly* what they're doing. So I think it's less bad to bend the rules on extents where FIEMAP_EXTENT_ENCODED is already set. In contrast, your suggestion would incorreectly report some parts of the file as standard extents (or holes) without FIEMAP_EXTENT_ENCODED, so it would be expected that the standard meaning would apply to those parts. - Eric _______________________________________________ Linux-f2fs-devel mailing list [email protected] https://lists.sourceforge.net/lists/listinfo/linux-f2fs-devel
