File sizes > 2 GB on isofs?

File sizes > 2 GB on isofs?

[Jeff Mahoney]

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I recently received a bug report regarding files on an iso9660
filesystem with sizes > 2 GB. mkisofs is apparently capable of creating
these filesystems, so I did a bit of research into if this was actually
valid or not.

It seems the iso9660/ecma119 spec doesn't specify the signedness of the
"32-bit number" for which they assign space to contain the file size.
There are tests in the kernel code to disallow file sizes > 2 GB, with
the apparent reason that there was, at some point, invalid CDs floating
around that hijacked the high byte of the file size field for some other
purpose.

With DVDs becoming widely popular for personal data storage, this 2 GB
limit will probably become more and more of an issue.

Currently, if a file is > 2 GB, 'cruft mode' is enabled which strips the
high byte off a file size. Attached is a patch that adds another
condition to that test: In order to enable 'cruft mode', the file size
must be larger than the volume size. A 3 GB file on a 700 MB CD is
certainly invalid, but a 3 GB file on a 4.7 GB DVD should be valid.

Might someone with a bit more familiarity with the spec be able to
comment on this?

Thanks.

- -Jeff

- --
Jeff Mahoney
SuSE Labs
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diff -rup linux-2.6.5-7.97/fs/isofs/inode.c linux-2.6.5-7.97.devel/fs/isofs/inode.c
--- linux-2.6.5-7.97/fs/isofs/inode.c	2004-07-02 10:41:26.000000000 -0400
+++ linux-2.6.5-7.97.devel/fs/isofs/inode.c	2004-08-10 13:26:51.796563112 -0400
@@ -1158,7 +1158,7 @@ static int isofs_read_level3_size(struct
 			de = tmpde;
 		}
 
-		inode->i_size += isonum_733(de->size);
+		inode->i_size += (unsigned)isonum_733(de->size);
 		if (i == 1)
 			ei->i_next_section_ino = f_pos;
 
@@ -1267,23 +1267,25 @@ static void isofs_read_inode(struct inod
 	ei->i_format_parm[1] = 0;
 	ei->i_format_parm[2] = 0;
 
-	ei->i_section_size = isonum_733 (de->size);
+	ei->i_section_size = (unsigned)isonum_733 (de->size);
 	if(de->flags[-high_sierra] & 0x80) {
 		if(isofs_read_level3_size(inode)) goto fail;
 	} else {
 		ei->i_next_section_ino = 0;
-		inode->i_size = isonum_733 (de->size);
+		inode->i_size = (unsigned)isonum_733 (de->size);
 	}
 
-	/*
-	 * The ISO-9660 filesystem only stores 32 bits for file size.
-	 * mkisofs handles files up to 2GB-2 = 2147483646 = 0x7FFFFFFE bytes
-	 * in size. This is according to the large file summit paper from 1996.
-	 * WARNING: ISO-9660 filesystems > 1 GB and even > 2 GB are fully
-	 *	    legal. Do not prevent to use DVD's schilling@fokus.gmd.de
-	 */
+	/* The ISO-9660 filesystem only stores 32 bits for file size.
+	 * mkisofs handles files up to 4 GB-1 = 0xFFFFFFFF bytes in size.
+	 * There used to be issues with some implementations hijacking the
+	 * high byte of the size field for some other purpose. In order to
+	 * allow for the full range of file sizes, yet still protect against
+	 * this, we check and see if the file size is larger than the size
+	 * of the entire volume.
+	 */
 	if ((inode->i_size < 0 || inode->i_size > 0x7FFFFFFE) &&
-	    sbi->s_cruft == 'n') {
+	    inode->i_size > (ISOFS_SB(sb)->s_nzones <<
+	    ISOFS_SB(sb)->s_log_zone_size) && sbi->s_cruft == 'n') {
 		printk(KERN_WARNING "Warning: defective CD-ROM.  "
 		       "Enabling \"cruft\" mount option.\n");
 		sbi->s_cruft = 'y';

Re: File sizes > 2 GB on isofs?

[Andi Kleen]

Jeff Mahoney <jeffm@suse.com> writes:

> With DVDs becoming widely popular for personal data storage, this 2 GB
> limit will probably become more and more of an issue.

That is what UDF was for created, wasn't it?

-Andi

Re: File sizes > 2 GB on isofs?

[Jeff Mahoney]

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Andi Kleen wrote:
| Jeff Mahoney <jeffm@suse.com> writes:
|
|
|>With DVDs becoming widely popular for personal data storage, this 2 GB
|>limit will probably become more and more of an issue.
|
|
| That is what UDF was for created, wasn't it?

That may well be true, but it's not a reason to not support the full
file size of iso9660 filesystems.

If my interpretation of the spec is correct, and I believe that it is,
then the max file size of an iso9660 filesystem is 4 GB. If it's not the
case, then mkisofs should be changed to not support such filesystems.
(Ignoring the recent fun with Joerg on LKML)

- -Jeff

- --
Jeff Mahoney
SuSE Labs
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