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);