nilfs2: allow future expansion of metadata read out via get info ioctl

Nilfs has some ioctl commands to read out metadata from meta data
files:

 - NILFS_IOCTL_GET_CPINFO for checkpoint file,
 - NILFS_IOCTL_GET_SUINFO for segment usage file, and
 - NILFS_IOCTL_GET_VINFO for Disk Address Transalation (DAT) file,
   respectively.

Every routine on these metadata files is implemented so that it allows
future expansion of on-disk format.  But, the above ioctl commands do
not support expansion even though nilfs_argv structure can handle
arbitrary size for data exchanged via ioctl.

This allows future expansion of the following structures which give
basic format of the "get information" ioctls:

 - struct nilfs_cpinfo
 - struct nilfs_suinfo
 - struct nilfs_vinfo

So, this introduces forward compatility of such ioctl commands.

In this patch, a sanity check in nilfs_ioctl_get_info() function is
changed to accept larger data structure [1], and metadata read
routines are rewritten so that they become compatible for larger
structures; the routines will just ignore the remaining fields which
the current version of nilfs doesn't know.

[1] The ioctl function already has another upper limit (PAGE_SIZE
    against a structure, which appears in nilfs_ioctl_wrap_copy
    function), and this will not cause security problem.

Signed-off-by: Ryusuke Konishi <konishi.ryusuke@lab.ntt.co.jp>

1 files changed, 11 insertions, 10 deletions

diff --git a/fs/nilfs2/dat.c b/fs/nilfs2/dat.c
index 1827f62c772d..0b2710e2d565 100644
--- a/fs/nilfs2/dat.c
+++ b/fs/nilfs2/dat.c
@@ -376,36 +376,37 @@ int nilfs_dat_translate(struct inode *dat, __u64 vblocknr, sector_t *blocknrp)
 	return ret;
 }
 
-ssize_t nilfs_dat_get_vinfo(struct inode *dat, struct nilfs_vinfo *vinfo,
+ssize_t nilfs_dat_get_vinfo(struct inode *dat, void *buf, unsigned visz,
 			    size_t nvi)
 {
 	struct buffer_head *entry_bh;
 	struct nilfs_dat_entry *entry;
+	struct nilfs_vinfo *vinfo = buf;
 	__u64 first, last;
 	void *kaddr;
 	unsigned long entries_per_block = NILFS_MDT(dat)->mi_entries_per_block;
 	int i, j, n, ret;
 
 	for (i = 0; i < nvi; i += n) {
-		ret = nilfs_palloc_get_entry_block(dat, vinfo[i].vi_vblocknr,
+		ret = nilfs_palloc_get_entry_block(dat, vinfo->vi_vblocknr,
 						   0, &entry_bh);
 		if (ret < 0)
 			return ret;
 		kaddr = kmap_atomic(entry_bh->b_page, KM_USER0);
 		/* last virtual block number in this block */
-		first = vinfo[i].vi_vblocknr;
+		first = vinfo->vi_vblocknr;
 		do_div(first, entries_per_block);
 		first *= entries_per_block;
 		last = first + entries_per_block - 1;
 		for (j = i, n = 0;
-		     j < nvi && vinfo[j].vi_vblocknr >= first &&
-			     vinfo[j].vi_vblocknr <= last;
-		     j++, n++) {
+		     j < nvi && vinfo->vi_vblocknr >= first &&
+			     vinfo->vi_vblocknr <= last;
+		     j++, n++, vinfo = (void *)vinfo + visz) {
 			entry = nilfs_palloc_block_get_entry(
-				dat, vinfo[j].vi_vblocknr, entry_bh, kaddr);
-			vinfo[j].vi_start = le64_to_cpu(entry->de_start);
-			vinfo[j].vi_end = le64_to_cpu(entry->de_end);
-			vinfo[j].vi_blocknr = le64_to_cpu(entry->de_blocknr);
+				dat, vinfo->vi_vblocknr, entry_bh, kaddr);
+			vinfo->vi_start = le64_to_cpu(entry->de_start);
+			vinfo->vi_end = le64_to_cpu(entry->de_end);
+			vinfo->vi_blocknr = le64_to_cpu(entry->de_blocknr);
 		}
 		kunmap_atomic(kaddr, KM_USER0);
 		brelse(entry_bh);