On Thu, Nov 10, 2022 at 03:12:21PM +0100, Niels de Vos wrote: > While more filesystems are getting support for fscrypt, it is useful to > be able to disable fscrypt for a selection of filesystems, while > enabling it for others. > > The new USE_FS_ENCRYPTION define gets picked up in > include/linux/fscrypt.h. This allows filesystems to choose to use the > empty function definitions, or the functional ones when fscrypt is to be > used with the filesystem. > > Using USE_FS_ENCRYPTION is a relatively clean approach, and requires > minimal changes to the filesystems supporting fscrypt. This RFC is > mostly for checking the acceptance of this solution, or if an other > direction is preferred. > > --- > > Niels de Vos (4): > fscrypt: introduce USE_FS_ENCRYPTION > fs: make fscrypt support an ext4 config option > fs: make fscrypt support a f2fs config option > fs: make fscrypt support a UBIFS config option So as others have pointed out, it doesn't seem worth the complexity to do this. For a bit of historical context, before Linux v5.1, we did have per-filesystem options for this: CONFIG_EXT4_ENCRYPTION, CONFIG_F2FS_FS_ENCRYPTION, and CONFIG_UBIFS_FS_ENCRYPTION. If you enabled one of these, it selected CONFIG_FS_ENCRYPTION to get the code in fs/crypto/. CONFIG_FS_ENCRYPTION was a tristate, so the code in fs/crypto/ could be built as a loadable module if it was only needed by filesystems that were loadable modules themselves. Having fs/crypto/ possibly be a loadable module was problematic, though, because it made it impossible to call into fs/crypto/ from built-in code such as fs/buffer.c, fs/ioctl.c, fs/libfs.c, fs/super.c, fs/iomap/direct-io.c, etc. So that's why we made CONFIG_FS_ENCRYPTION into a bool. At the same time, we decided to simplify the kconfig options by removing the per-filesystem options so that it worked like CONFIG_QUOTA, CONFIG_FS_DAX, CONFIG_FS_POSIX_ACL, etc. I suppose we *could* have *just* changed CONFIG_FS_ENCRYPTION to a bool to solve the first problem, and kept the per-filesystem options. I think that wouldn't have made a lot of sense, though, for the reasons that Ted has already covered. A further point, beyond what Ted has already covered, is that non-filesystem-specific code can't honor filesystem-specific options. So e.g. if you had a filesystem with encryption disabled by kconfig, that then called into fs/iomap/direct-io.c to process an I/O request, it could potentially still call into fs/crypto/ to enable encryption on that I/O request, since fs/iomap/direct-io.c would think that encryption support is enabled. Granted, that *should* never actually happen, because this would only make a difference on encrypted files, and the filesystem shouldn't have allowed an encrypted file to be opened if it doesn't have encryption support enabled. But it does seem a bit odd, given that it would go against the goal of compiling out all encryption code for a filesystem. - Eric
