ecryptfs is unmaintained and untested

[Matthew Wilcox <willy@infradead.org>]

On Mon, Oct 28, 2024 at 02:18:45PM +0000, Arnd Bergmann wrote:
> The ecryptfs file system uses functions from fs/buffer.c that
> are only available when CONFIG_BUFFER_HEAD is enabled:
> 
> ld.lld-20: error: undefined symbol: block_dirty_folio
> >>>               vmlinux.o:(ecryptfs_aops)
> ld.lld-20: error: undefined symbol: block_invalidate_folio
> >>>               vmlinux.o:(ecryptfs_aops)
> 
> When CONFIG_BLOCK is turned off completely, this is not needed,
> so add a conditional 'select BUFFER_HEAD'.

The comment says it doesn't work without CONFIG_BLOCK:

        /*
         * XXX: This is pretty broken for multiple reasons: ecryptfs does not
         * actually use buffer_heads, and ecryptfs will crash without
         * CONFIG_BLOCK.  But it matches the behavior before the default for
         * address_space_operations without the ->dirty_folio method was
         * cleaned up, so this is the best we can do without maintainer
         * feedback.

This comment has been there since June 2021, so I think we can just
delete ecryptfs now?

If we can't delete it for some reason, I think we can use
filemap_dirty_folio() and remove the setting of invalidate_folio()
as block_invalidate_folio() is a no-op if there are no folio_buffers.
ie this in lieu of your patch:

+++ b/fs/ecryptfs/mmap.c
@@ -514,17 +514,9 @@ static sector_t ecryptfs_bmap(struct address_space *mapping, sector_t block)
 
 const struct address_space_operations ecryptfs_aops = {
        /*
-        * XXX: This is pretty broken for multiple reasons: ecryptfs does not
-        * actually use buffer_heads, and ecryptfs will crash without
-        * CONFIG_BLOCK.  But it matches the behavior before the default for
-        * address_space_operations without the ->dirty_folio method was
-        * cleaned up, so this is the best we can do without maintainer
-        * feedback.
+        * XXX: This entire filesystem is unmaintained and untested.
         */
-#ifdef CONFIG_BLOCK
-       .dirty_folio    = block_dirty_folio,
-       .invalidate_folio = block_invalidate_folio,
-#endif
+       .dirty_folio = filemap_dirty_folio,
        .writepages = ecryptfs_writepages,
        .read_folio = ecryptfs_read_folio,
        .write_begin = ecryptfs_write_begin,