On 26/04/21 6:07 pm, Matthew Wilcox wrote:
On Mon, Apr 26, 2021 at 05:27:51PM +0530, Shreeya Patel wrote:
On 26/04/21 6:04 am, Matthew Wilcox wrote:
On Mon, Apr 26, 2021 at 04:01:05AM +0530, Shreeya Patel wrote:
exFAT filesystem does not support the following character codes
0x0000 - 0x001F ( Control Codes ), /, ?, :, ", \, *, <, |, >
ummm ...
-# Fake slash?
-setf "urk\xc0\xafmoo" "FAKESLASH"
That doesn't use any of the explained banned characters. It uses 0xc0,
0xaf.
Now, in utf-8, that's an nonconforming sequence. "The Unicode and UCS
standards require that producers of UTF-8 shall use the shortest form
possible, for example, producing a two-byte sequence with first byte 0xc0
is nonconforming. Unicode 3.1 has added the requirement that conforming
programs must not accept non-shortest forms in their input."
So is it that exfat is rejecting nonconforming sequences? Or is it
converting the nonconforming sequence from 0xc0 0xaf to the conforming
sequence 0x2f, and then rejecting it (because it's '/')?
No, I don't think exfat is not converting nonconforming sequence from 0xc0
0xaf
to the conforming sequence 0x2f.
Because I get different outputs when tried with both ways.
When I create a file with "urk\xc0\xafmoo", I get output as "Operation not
permitted"
and when I create it as "urk\x2fmoo", it gives "No such file or directory
error" or
you can consider this error as "Invalid argument"
( because that's what I get when I try for other characters like |, :, ?,
etc )
I think we need to understand this before skipping the test. Does it
also fail, eg, on cifs, vfat, jfs or udf?
I tested it for VFAT, UDF and JFS and following are the results.
1. VFAT ( as per wikipedia 0x00-0x1F 0x7F " * / : < > ? \ | are reserved
characters)
For \x2f - /var/mnt/scratch/test-453/urk/moo.txt: No such file or directory
For \xc0\xaf) - /var/mnt/scratch/test-453/urk��moo.txt: Invalid argument
Also gives error for Box filename
( this is very much similar to exfat, the only difference is that I do
not get Operation not permitted when
using \xc0\xaf, instead it gives invalid argument.)
2. UDF ( as per wikipedia - only NULL cannot be used )
For \x2f - /var/mnt/scratch/test-453/urk/moo.txt: No such file or directory
For \xc0\xaf - creates filename something like this 'urk??moo.txt' and
does not throw any error.
( But this seems to be invalid and should have thrown some error)
Also gives error for dotdot entry.
I am not sure why UDF was giving error for / and dot dot entry but then
I read the following for UDF in one of the man pages which justifies the
above errors I think
"Invalid characters such as "NULL" and "/" and invalid file
names such as "." and ".." will be translated according to
the following rule:
Replace the invalid character with an "_," then append the
file name with # followed by a 4 digit hex representation of
the 16-bit CRC of the original FileIdentifier. For example,
the file name ".." will become "__#4C05" "
Source - http://www-it.desy.de/cgi-bin/man-cgi?udfs+7
3. JFS ( as per Wikipedia NULL cannot be used )
For \x2f - /var/mnt/scratch/test-453/urk/moo.txt: No such file or directory
For \xc0\xaf - Works fine
Again not sure why / is failing here. Did not find much resource about
the restricted filenames for JFS.
So as per above all the results, it seems like using \x2f fails for all
but \xc0\xaf does work for JFS.
Box filename also fails with "Invalid argument" error.
