[PATCH v2 0/4] fs: return error pointers from ->get_link() on failure

[Sascha Hauer <s.hauer@pengutronix.de>]

Like in Linux, the callers of ->get_link() expect an error pointer when
the link can't be read: readlinkat() checks the result only with
IS_ERR() before copying from it, and path lookup takes NULL to mean that
the link has already been followed and continues from the directory
containing the link. barebox has no nd_jump_link(), so a NULL from
->get_link() is never legitimate there.

9p and nfs already return error pointers, and the squashfs series posted
separately converts squashfs_get_link(). This series converts the
remaining file systems:

- legacy returned NULL when the driver's readlink failed.
- cramfs and ext4 checked their read helpers for return values these
  never produce, so a link that couldn't be read was returned as a valid,
  partly zeroed link and stayed cached in inode->i_link.

For cramfs, that needs cramfs_read_file() to stop at a block that fails
to decompress in the first place: it stored the error in a size_t and
returned whatever the block buffer held instead, for symlinks and
regular files alike. The first patch fixes that.

Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>
---
Changes in v2:
- New patch "fs: cramfs: don't ignore decompression errors": the error
  check in cramfs_read_file() could never fire, so cramfs_get_link()
  couldn't see a failed read either
- Link to v1: https://lore.barebox.org/20261102-fs-getlink-fixes-v1-0-c2816b3f5ca8@pengutronix.de

---
Sascha Hauer (4):
      fs: cramfs: don't ignore decompression errors
      fs: cramfs: return an error pointer from cramfs_get_link()
      fs: ext4: return an error pointer from ext_get_link()
      fs: legacy: return an error pointer from legacy_get_link()

 fs/cramfs/cramfs.c    | 11 +++++++----
 fs/ext4/ext_barebox.c |  3 ++-
 fs/legacy.c           |  2 +-
 3 files changed, 10 insertions(+), 6 deletions(-)
---
base-commit: f2e574b9c63c6da07a06179a868cae8a471ec176
change-id: 20261102-fs-getlink-fixes-d634fd50d1f9

Best regards,
-- 
Sascha Hauer <s.hauer@pengutronix.de>