[PATCH RFC 8/8] ext4: Add a per-file provision override xattr

Sarthak Kukreti
2022-09-15T16:50:03Z

From: Sarthak Kukreti <sarthakkukreti@chromium.org>

Adds a per-file provision override that allows select files to
override the per-mount setting for provisioning blocks on allocation.

This acts as a mechanism to allow mounts using provision to
replicate the current behavior for fallocate() and only preserve
space at the filesystem level.

Signed-off-by: Sarthak Kukreti <sarthakkukreti@chromium.org>
---
fs/ext4/extents.c | 32 ++++++++++++++++++++++++++++++++
fs/ext4/xattr.h | 1 +
2 files changed, 33 insertions(+)

diff --git a/fs/ext4/extents.c b/fs/ext4/extents.c
index 746213b5ec3d..a9ed908b2ebe 100644
--- a/fs/ext4/extents.c
+++ b/fs/ext4/extents.c
@@ -4424,6 +4424,26 @@ int ext4_ext_truncate(handle_t *handle, struct inode *inode)
return err;
}

+int ext4_provision_support(struct inode *inode)
+{
+ char provision;
+ int ret =
+ ext4_xattr_get(inode, EXT4_XATTR_INDEX_TRUSTED,
+ EXT4_XATTR_NAME_PROVISION_POLICY, &provision, 1);
+
+ if (ret < 0)
+ return ret;
+
+ switch (provision) {
+ case 'y':
+ return 1;
+ case 'n':
+ return 0;
+ default:
+ return -EINVAL;
+ }
+}
+
static int ext4_alloc_file_blocks(struct file *file, ext4_lblk_t offset,
ext4_lblk_t len, loff_t new_size,
int flags)
@@ -4436,12 +4456,24 @@ static int ext4_alloc_file_blocks(struct file *file, ext4_lblk_t offset,
struct ext4_map_blocks map;
unsigned int credits;
loff_t epos;
+ bool provision = false;
+ int file_provision_override = -1;

/*
* Attempt to provision file blocks if the mount is mounted with
* provision.
*/
if (test_opt2(inode->i_sb, PROVISION))
+ provision = true;
+
+ /*
+ * Use file-specific override, if available.
+ */
+ file_provision_override = ext4_provision_support(inode);
+ if (file_provision_override >= 0)
+ provision &= file_provision_override;
+
+ if (provision)
flags |= EXT4_GET_BLOCKS_PROVISION;

BUG_ON(!ext4_test_inode_flag(inode, EXT4_INODE_EXTENTS));
diff --git a/fs/ext4/xattr.h b/fs/ext4/xattr.h
index 824faf0b15a8..69e97f853b0c 100644
--- a/fs/ext4/xattr.h
+++ b/fs/ext4/xattr.h
@@ -140,6 +140,7 @@ extern const struct xattr_handler ext4_xattr_security_handler;
extern const struct xattr_handler ext4_xattr_hurd_handler;

#define EXT4_XATTR_NAME_ENCRYPTION_CONTEXT "c"
+#define EXT4_XATTR_NAME_PROVISION_POLICY "provision"

/*
* The EXT4_STATE_NO_EXPAND is overloaded and used for two purposes.
--
2.31.0