quick question about filename length

quick question about filename length

[Chris Walker]

Hello,

I see that
#define MAXNAMELEN  256

Is this the maximum length of the filename with full path?  Or is this
just the name of the file?

Many thanks!
Chris

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Re: quick question about filename length

[Eric Sandeen]

Chris Walker wrote:
> Hello,
> 
> I see that
> #define MAXNAMELEN  256
> 
> Is this the maximum length of the filename with full path?  Or is this
> just the name of the file?
> 
> Many thanks!
> Chris

/*
 * MAXNAMELEN is the length (including the terminating null) of
 * the longest permissible file (component) name.
 */
#define MAXNAMELEN      256

"component" means path component.  So just the name of the file or dir
in the path.

See also how it's used in xfs_vn_lookup() for example:

        if (dentry->d_name.len >= MAXNAMELEN)
                return ERR_PTR(-ENAMETOOLONG);

a dentry is one component of the path, not the entire path.

-Eric

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Re: quick question about filename length

[Chris Walker]

Thanks for you quick reply, Eric.

I have a user who is having filenames (path+filename) cut off at 255
characters midway through a simulation -- but the problem must be
elsewhere

Thanks again,
Chris

On Sat, May 16, 2009 at 1:04 PM, Eric Sandeen <sandeen@sandeen.net> wrote:
> Chris Walker wrote:
>> Hello,
>>
>> I see that
>> #define MAXNAMELEN  256
>>
>> Is this the maximum length of the filename with full path?  Or is this
>> just the name of the file?
>>
>> Many thanks!
>> Chris
>
> /*
>  * MAXNAMELEN is the length (including the terminating null) of
>  * the longest permissible file (component) name.
>  */
> #define MAXNAMELEN      256
>
> "component" means path component.  So just the name of the file or dir
> in the path.
>
> See also how it's used in xfs_vn_lookup() for example:
>
>        if (dentry->d_name.len >= MAXNAMELEN)
>                return ERR_PTR(-ENAMETOOLONG);
>
> a dentry is one component of the path, not the entire path.
>
> -Eric
>

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Re: quick question about filename length

[Christoph Hellwig]

On Sat, May 16, 2009 at 02:06:22PM -0400, Chris Walker wrote:
> Thanks for you quick reply, Eric.
> 
> I have a user who is having filenames (path+filename) cut off at 255
> characters midway through a simulation -- but the problem must be
> elsewhere

XFS doesn't actually see the whole filename in normal operation (except
for copying out the data out of symbolic links), as the resolution to
individual components is done by the VFS.   Long file name should work
just fine on Linux and do in my test.  Maybe some buffer is sized using
incorrect in userspace?

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Re: quick question about filename length

[Martin Steigerwald]

Am Samstag 16 Mai 2009 schrieb Christoph Hellwig:
> On Sat, May 16, 2009 at 02:06:22PM -0400, Chris Walker wrote:
> > Thanks for you quick reply, Eric.
> >
> > I have a user who is having filenames (path+filename) cut off at 255
> > characters midway through a simulation -- but the problem must be
> > elsewhere
>
> XFS doesn't actually see the whole filename in normal operation (except
> for copying out the data out of symbolic links), as the resolution to
> individual components is done by the VFS.   Long file name should work
> just fine on Linux and do in my test.  Maybe some buffer is sized using
> incorrect in userspace?

And while a link name itself also can't be longer than about 256 
characters (I only tested 250 and 260), a link can point to a longer 
path ;-):

martin@shambhala:~/Zeit> mkdir -p 
$(ruby -e 'puts "1234567890"*25')/$(ruby -e 'puts "1234567890"*25')
martin@shambhala:~/Zeit> ln -s 
$(ruby -e 'puts "1234567890"*25')/$(ruby -e 'puts "1234567890"*25') 
testlink
martin@shambhala:~/Zeit> ls -l testlink
lrwxrwxrwx 1 martin martin 501 16. Mai 23:40 testlink -> 
12345678901234567890123456789012345678901234567890123456789[...]
martin@shambhala:~/Zeit> (df -hT . | grep -q xfs) && echo "Is XFS"
Is XFS

-- 
Martin 'Helios' Steigerwald - http://www.Lichtvoll.de
GPG: 03B0 0D6C 0040 0710 4AFA  B82F 991B EAAC A599 84C7

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