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Subject[PATCH 3/3] [fs/sysv] V7: Add support for non-PDP11 v7 filesystems
Date
A mount-time option was added that makes it possible to override the
endianness and an attempt is made to autodetect it (which seems easy,
given the disk addresses are 3-byte.

No attempt is made to detect big-endian filesystems -- were there any?
Tested with PDP-11 v7 filesystems and PC-IX maintenance floppy.

Cc: Christoph Hellwig <hch@lst.de>
Signed-off-by: Lubomir Rintel <lkundrak@v3.sk>
---
fs/sysv/super.c | 116 +++++++++++++++++++++++++++++++++++++----------
include/linux/sysv_fs.h | 6 +-
2 files changed, 95 insertions(+), 27 deletions(-)
diff --git a/fs/sysv/super.c b/fs/sysv/super.c
index 17ac83d..9cd5be0 100644
--- a/fs/sysv/super.c
+++ b/fs/sysv/super.c
@@ -24,6 +24,7 @@
#include <linux/init.h>
#include <linux/slab.h>
#include <linux/buffer_head.h>
+#include <linux/parser.h>
#include "sysv.h"

/*
@@ -435,12 +436,55 @@ Ebadsize:
goto failed;
}

-static int v7_fill_super(struct super_block *sb, void *data, int silent)
+static int v7_sanity_check(struct super_block *sb, struct buffer_head *bh)
{
- struct sysv_sb_info *sbi;
- struct buffer_head *bh, *bh2 = NULL;
struct v7_super_block *v7sb;
struct sysv_inode *v7i;
+ struct buffer_head *bh2;
+ struct sysv_sb_info *sbi;
+
+ sbi = sb->s_fs_info;
+
+ /* plausibility check on superblock */
+ v7sb = (struct v7_super_block *) bh->b_data;
+ if (fs16_to_cpu(sbi, v7sb->s_nfree) > V7_NICFREE ||
+ fs16_to_cpu(sbi, v7sb->s_ninode) > V7_NICINOD ||
+ fs32_to_cpu(sbi, v7sb->s_fsize) > V7_MAXSIZE)
+ return 0;
+
+ /* plausibility check on root inode: it is a directory,
+ with a nonzero size that is a multiple of 16 */
+ if ((bh2 = sb_bread(sb, 2)) == NULL) {
+ return 0;
+ }
+
+ v7i = (struct sysv_inode *)(bh2->b_data + 64);
+ if ((fs16_to_cpu(sbi, v7i->i_mode) & ~0777) != S_IFDIR ||
+ (fs32_to_cpu(sbi, v7i->i_size) == 0) ||
+ (fs32_to_cpu(sbi, v7i->i_size) & 017) ||
+ (fs32_to_cpu(sbi, v7i->i_size) > V7_NFILES *
+ sizeof (struct sysv_dir_entry))) {
+ brelse(bh2);
+ return 0;
+ }
+
+ brelse(bh2);
+ return 1;
+}
+
+enum { Opt_err, Opt_bytesex_pdp, Opt_bytesex_le, Opt_bytesex_be };
+
+static const match_table_t v7_tokens = {
+ {Opt_bytesex_pdp, "bytesex=pdp"},
+ {Opt_bytesex_le, "bytesex=le"},
+ {Opt_bytesex_be, "bytesex=be"},
+ {Opt_err, NULL}
+};
+
+static int v7_fill_super(struct super_block *sb, void *data, int silent)
+{
+ struct sysv_sb_info *sbi;
+ struct buffer_head *bh;

if (440 != sizeof (struct v7_super_block))
panic("V7 FS: bad super-block size");
@@ -454,7 +498,6 @@ static int v7_fill_super(struct super_block *sb, void *data, int silent)
sbi->s_sb = sb;
sbi->s_block_base = 0;
sbi->s_type = FSTYPE_V7;
- sbi->s_bytesex = BYTESEX_PDP;
sb->s_fs_info = sbi;

sb_set_blocksize(sb, 512);
@@ -466,26 +509,51 @@ static int v7_fill_super(struct super_block *sb, void *data, int silent)
goto failed;
}

- /* plausibility check on superblock */
- v7sb = (struct v7_super_block *) bh->b_data;
- if (fs16_to_cpu(sbi, v7sb->s_nfree) > V7_NICFREE ||
- fs16_to_cpu(sbi, v7sb->s_ninode) > V7_NICINOD ||
- fs32_to_cpu(sbi, v7sb->s_fsize) > V7_MAXSIZE)
- return 0;
+ if (data) {
+ substring_t args[MAX_OPT_ARGS];
+ char *p;
+
+ while ((p = strsep ((char **)&data, ",")) != NULL) {
+ int token;
+ if (!*p)
+ continue;
+ token = match_token(p, v7_tokens, args);
+ switch (token) {
+ case Opt_bytesex_pdp:
+ sbi->s_bytesex = BYTESEX_PDP;
+ break;
+ case Opt_bytesex_le:
+ sbi->s_bytesex = BYTESEX_LE;
+ break;
+ case Opt_bytesex_be:
+ sbi->s_bytesex = BYTESEX_BE;
+ break;
+ default:
+ /* An unrecognized option */
+ goto failed;
+ }
+ }
+ }

- /* plausibility check on root inode: it is a directory,
- with a nonzero size that is a multiple of 16 */
- if ((bh2 = sb_bread(sb, 2)) == NULL)
- goto failed;
- v7i = (struct sysv_inode *)(bh2->b_data + 64);
- if ((fs16_to_cpu(sbi, v7i->i_mode) & ~0777) != S_IFDIR ||
- (fs32_to_cpu(sbi, v7i->i_size) == 0) ||
- (fs32_to_cpu(sbi, v7i->i_size) & 017)
- (fs32_to_cpu(sbi, v7i->i_size) > V7_NFILES *
- sizeof (struct sysv_dir_entry))) {
- goto failed;
- brelse(bh2);
- bh2 = NULL;
+ /* Endianness overridden by a mount option */
+ if (sbi->s_bytesex) {
+ if (!v7_sanity_check (sb, bh))
+ goto failed;
+ goto detected;
+ }
+
+ /* Try PDP-11 UNIX */
+ sbi->s_bytesex = BYTESEX_PDP;
+ if (v7_sanity_check (sb, bh))
+ goto detected;
+
+ /* Try PC/IX, v7/x86 */
+ sbi->s_bytesex = BYTESEX_LE;
+ if (v7_sanity_check (sb, bh))
+ goto detected;
+
+ goto failed;
+detected:

sbi->s_bh1 = bh;
sbi->s_bh2 = bh;
@@ -493,7 +561,7 @@ static int v7_fill_super(struct super_block *sb, void *data, int silent)
return 0;

failed:
- brelse(bh2);
+ printk("VFS: could not find a valid V7 on %s.\n", sb->s_id);
brelse(bh);
kfree(sbi);
return -EINVAL;
diff --git a/include/linux/sysv_fs.h b/include/linux/sysv_fs.h
index 0a7a232..e47d6d9 100644
--- a/include/linux/sysv_fs.h
+++ b/include/linux/sysv_fs.h
@@ -155,9 +155,9 @@ struct v7_super_block {
* directory. Thus, if we see anything higher, we just probably got the
* endiannes wrong. */
#define V7_NFILES 1024
-/* Indirect blocks hold just three-byte addresses, therefore if see a file
- * system whose length has the most significant byte non-zero something is
- * most likely wrong (not a filesystem, bad bytesex). */
+/* The disk addresses are three-byte (despite direct block addresses being
+ * aligned word-wise in inode). If the most significant byte is non-zero,
+ * something is most likely wrong (not a filesystem, bad bytesex). */
#define V7_MAXSIZE 0x00ffffff

/* Coherent super-block data on disk */
--
1.6.5.2


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