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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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