[PATCH v2] hfs: report errors when extending files with setattr

[Hengyu Liang]

hfs_inode_setattr() sets i_size and calls hfs_file_truncate() to change
the allocation. If expansion fails, hfs_file_truncate() restores i_size
to the allocated size, but its void return type leaves setattr reporting
success.

On a freshly formatted 64 MiB HFS volume, ftruncate() to 128 MiB returns
zero while the file remains empty. When the requested size fits within
the volume but exceeds the free space, it also returns zero, leaving
the file only partially extended.

Call generic_cont_expand_simple() when growing a file and propagate its
error. Keep truncate_setsize() and hfs_file_truncate() in the shrinking
path. This makes failed extensions report EFBIG or ENOSPC.

Signed-off-by: Hengyu Liang <hengyul@xxxxxxxxxx>
---
Changes in v2:
- Keep truncate_setsize() and hfs_file_truncate() in the shrinking path,
  as suggested by Viacheslav Dubeyko.
- Replace the generic/736 and fsx runs with a comparison of the whole
  xfstests set selected for HFS, as requested.

v1: https://lore.kernel.org/r/20261017160612.3740256-1-hengyul@xxxxxxxxxx

Compared unpatched and patched v7.3-rc7 with identical KASAN configs.
All 805 tests selected for HFS by "check -n -g all" were attempted,
using freshly formatted 2 GiB test and scratch volumes for each case:
                passed  failed  not run
  unpatched       109      27      669
  v2              109      27      669

The different results were generic/113, /394, /464 and /795. /113 and
/464 passed and failed in replays on the unpatched kernel, and the /113
failures are the same existing workqueue warning from hfs_file_fsync().
/795 failed on all three kernels in replays. On the 2 GiB volume, /394
passes without the fix only because ftruncate() returns success after a
partial extension; v1 and v2 report ENOSPC. It passes on all three
kernels with a 4 GiB volume.

Also ran 39 functional and 18 recovery cases per kernel on 32/64/128 MiB
volumes. Content and read-only remount checks passed on unpatched, v1
and v2 kernels. All three had the same 12 post-ENOSPC fsck failures;
recovery fsck checks were clean.

Functional/recovery cases and generic/394 were repeated on unpatched
and v2 kernels at the hfs 7.4 merge (dd7b15aeac80), with the same results.

 fs/hfs/inode.c | 10 ++++++++--
 1 file changed, 8 insertions(+), 2 deletions(-)

diff --git a/fs/hfs/inode.c b/fs/hfs/inode.c
index 2aef3c36a150..9bdaa60fc392 100644
--- a/fs/hfs/inode.c
+++ b/fs/hfs/inode.c
@@ -684,8 +684,14 @@ int hfs_inode_setattr(struct mnt_idmap *idmap, struct dentry *dentry,
 		if (error)
 			return error;
 
-		truncate_setsize(inode, attr->ia_size);
-		hfs_file_truncate(inode);
+		if (attr->ia_size > inode->i_size) {
+			error = generic_cont_expand_simple(inode, attr->ia_size);
+			if (error)
+				return error;
+		} else {
+			truncate_setsize(inode, attr->ia_size);
+			hfs_file_truncate(inode);
+		}
 		inode_set_mtime_to_ts(inode, inode_set_ctime_current(inode));
 	}
 
-- 
2.53.0