fs/ntfs3: Add support for the compression attribute

Support added for empty files and directories only.

Signed-off-by: Konstantin Komarov <almaz.alexandrovich@paragon-software.com>

1 files changed, 71 insertions, 0 deletions

diff --git a/fs/ntfs3/attrib.c b/fs/ntfs3/attrib.c
index d2a9cd963429..0763202d00c9 100644
--- a/fs/ntfs3/attrib.c
+++ b/fs/ntfs3/attrib.c
@@ -2605,3 +2605,74 @@ int attr_force_nonresident(struct ntfs_inode *ni)
 
 	return err;
 }
+
+/*
+ * Change the compression of data attribute
+ */
+int attr_set_compress(struct ntfs_inode *ni, bool compr)
+{
+	struct ATTRIB *attr;
+	struct mft_inode *mi;
+
+	attr = ni_find_attr(ni, NULL, NULL, ATTR_DATA, NULL, 0, NULL, &mi);
+	if (!attr)
+		return -ENOENT;
+
+	if (is_attr_compressed(attr) == !!compr) {
+		/* Already required compressed state. */
+		return 0;
+	}
+
+	if (attr->non_res) {
+		u16 run_off;
+		u32 run_size;
+		char *run;
+
+		if (attr->nres.data_size) {
+			/*
+			 * There are rare cases when it possible to change
+			 * compress state without big changes.
+			 * TODO: Process these cases.
+			 */
+			return -EOPNOTSUPP;
+		}
+
+		run_off = le16_to_cpu(attr->nres.run_off);
+		run_size = le32_to_cpu(attr->size) - run_off;
+		run = Add2Ptr(attr, run_off);
+
+		if (!compr) {
+			/* remove field 'attr->nres.total_size'. */
+			memmove(run - 8, run, run_size);
+			run_off -= 8;
+		}
+
+		if (!mi_resize_attr(mi, attr, compr ? +8 : -8)) {
+			/*
+			 * Ignore rare case when there are no 8 bytes in record with attr.
+			 * TODO: split attribute.
+			 */
+			return -EOPNOTSUPP;
+		}
+
+		if (compr) {
+			/* Make a gap for 'attr->nres.total_size'. */
+			memmove(run + 8, run, run_size);
+			run_off += 8;
+			attr->nres.total_size = attr->nres.alloc_size;
+		}
+		attr->nres.run_off = cpu_to_le16(run_off);
+	}
+
+	/* Update data attribute flags. */
+	if (compr) {
+		attr->flags |= ATTR_FLAG_COMPRESSED;
+		attr->nres.c_unit = NTFS_LZNT_CUNIT;
+	} else {
+		attr->flags &= ~ATTR_FLAG_COMPRESSED;
+		attr->nres.c_unit = 0;
+	}
+	mi->dirty = true;
+
+	return 0;
+}