On Mon, 15 Jan 2001, Robert Reither wrote:
> I encounted really bad problems with 2048 Bytes/sec MO-Drive.
> I'm using an Olympus PowerMO 640.
> MO was formated with FAT32.
>
> i try to read a file from it (used : 'pico /mo/file.txt') ...
> And got a nice crash : Segmentation Fault
Even worse. Trying to read any file on a 2k hwblk FAT yields an oops
actually.
> OK, was easy to find this bug, fs/fat/cvf.c has a bug in bigblock_cvf struct
> the field with the read function was a NULL.
> I changed this to generic_file_read (like with default blocksize), and
> tested it. First seemed to work fine, but :
>
> If i write a file to an empty MO-Disk, the start-cluster is 2 in the
> table. But the real data was written to (and also read from)
> cluster 33 by linux !
The generic routines do not handle the (rather braindead) case of
hwblksize > logical blksize. FAT uses a logical block (sector/whatever
you like to name it) size of 512 byte, which obviously sucks. Now,
generic_file_read miscalculates the blocks it has to get, but in the same
way as generic_file_write, so two errors yield a working setup, but only
for data you wrote with a buggy kernel. You won't be able to access any
previously written data in this way.
A few days ago, I posted the below patch as a quick band-aid to get at
least the read() part back to a working state again. It also disables the
equally dysfunctional mmap() on 2k media. It ought to disable write() as
well, but I didn't bother. Just don't do it. It's probably best to use the
patch to backup your data and reformat your MOs with a sane fs. Run, don't
walk. ;-)
Regards,
Daniel.
--[snip]--
--- cvf.c.vanilla Mon Jan 1 22:46:20 2001
+++ cvf.c Mon Jan 1 23:31:23 2001
@@ -51,6 +51,9 @@
const char *buf,
size_t count,
loff_t *ppos);
+ssize_t bigblock_fat_file_read(struct file *filp, char *buf, size_t count,
+ loff_t *ppos);
+
struct cvf_format default_cvf = {
0, /* version - who cares? */
@@ -92,7 +95,7 @@
default_fat_access,
NULL,
default_fat_bmap,
- NULL,
+ bigblock_fat_file_read,
default_fat_file_write,
NULL,
NULL
--- file.c.vanilla Mon Jan 1 22:46:26 2001
+++ file.c Tue Jan 16 00:15:16 2001
@@ -4,6 +4,9 @@
* Written 1992,1993 by Werner Almesberger
*
* regular file handling primitives for fat-based filesystems
+ *
+ * 2001-1-1 Daniel Kobras <[EMAIL PROTECTED]>:
+ * Added quick&dirty read operation for large sector media.
*/
#define ASC_LINUX_VERSION(V, P, S) (((V) * 65536) + ((P) * 256) + (S))
@@ -114,6 +117,56 @@
return retval;
}
+/* This is a hack. No readahead and other fancy stuff, but hopefully enough
+ * to get MOs working again. [dk]
+ * FIXME: Not sure whether I got error checking right.
+ */
+ssize_t bigblock_fat_file_read(struct file *filp, char *buf, size_t count,
+ loff_t *ppos)
+{
+ struct inode *inode = filp->f_dentry->d_inode;
+ int phys, pos;
+ struct buffer_head *bh;
+ size_t to_go, done;
+ char *buf_start = buf;
+
+ /* Taken from 2.2 source. */
+ if (!S_ISREG(inode->i_mode) && !S_ISLNK(inode->i_mode))
+ return -EINVAL;
+
+ if (*ppos > inode->i_size || !count)
+ return 0;
+
+ if (inode->i_size - *ppos < count)
+ count = inode->i_size - *ppos;
+
+ pos = *ppos>>SECTOR_BITS;
+ to_go = SECTOR_SIZE - (*ppos&(SECTOR_SIZE-1));
+ goto _start;
+
+ do {
+ to_go = SECTOR_SIZE;
+_start:
+ phys = fat_bmap(inode, pos++);
+ if (!phys)
+ return -EIO;
+ bh = fat_bread(inode->i_sb, phys);
+ if (!bh)
+ return -EIO;
+ done = to_go > count ? count : to_go;
+ if (copy_to_user(buf, bh->b_data, done)) {
+ fat_brelse(inode->i_sb, bh);
+ return -EFAULT;
+ }
+ fat_brelse(inode->i_sb, bh);
+ buf += done;
+ *ppos += done;
+ } while ((count -= done));
+
+ return buf - buf_start;
+}
+
+
void fat_truncate(struct inode *inode)
{
struct msdos_sb_info *sbi = MSDOS_SB(inode->i_sb);
--- inode.c.vanilla Tue Jan 2 00:36:18 2001
+++ inode.c Tue Jan 2 00:22:04 2001
@@ -820,6 +820,9 @@
inode->i_size = CF_LE_L(de->size);
inode->i_op = &fat_file_inode_operations;
inode->i_fop = &fat_file_operations;
+ /* FIXME: mmap is broken with large hwblocks! [dk] */
+ if (sb->s_blocksize > 512)
+ inode->i_fop->mmap = NULL;
inode->i_mapping->a_ops = &fat_aops;
MSDOS_I(inode)->mmu_private = inode->i_size;
}
-
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