Two questions regarding Opening files within Kernel!

Two questions regarding Opening files within Kernel!

[JanuGerman]

Hi Every one,

  I have got two questions regarding opening files within the Linux kernel. If some body can help me, in sorting out this problem, i will be very thankful.

1)   I have just a file path with me, an absolute path, but no dentry, no inode, no vfsmount object, which function i can call to get a "file" object associated with the absoulte file path. I have surfed arround the source code especially fs/open.c and some other files, but each function requires a parameter "mode" and "fd" beside file path. Actually, i was confuse about the "mode" parameter (and its differece with "flag"), like what to send, and secondly for "fd", i am not sure, what value to send as there is no file infact and only file path exists. Any idea?

2) Any functionality within linux kernel source code, to read one line per file? or some indirect way to set buffer size for one read?. That is, any existing header file for doing text I/O rather than binary within the kernel source code?

Thanks,
JG


		
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Re: Two questions regarding Opening files within Kernel!

[Roland Kuhn]

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Hi!

On 7 Apr 2007, at 08:58, JanuGerman wrote:

> 1)   I have just a file path with me, an absolute path, but no  
> dentry, no inode, no vfsmount object, which function i can call to  
> get a "file" object associated with the absoulte file path. I have  
> surfed arround the source code especially fs/open.c and some other  
> files, but each function requires a parameter "mode" and "fd"  
> beside file path. Actually, i was confuse about the "mode"  
> parameter (and its differece with "flag"), like what to send, and  
> secondly for "fd", i am not sure, what value to send as there is no  
> file infact and only file path exists. Any idea?
>
No, but I'm no guru either.

> 2) Any functionality within linux kernel source code, to read one  
> line per file? or some indirect way to set buffer size for one  
> read?. That is, any existing header file for doing text I/O rather  
> than binary within the kernel source code?
>
Do you have a compelling reason for not letting userspace feed the  
file to your driver? That would be the natural and much easier way, I  
suppose...

Ciao,
                     Roland

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Re: Two questions regarding Opening files within Kernel!

[Jan Engelhardt]

On Apr 7 2007 06:58, JanuGerman wrote:
>Hi Every one,
>
>  I have got two questions regarding opening files within the Linux 
>  kernel. If some body can help me, in sorting out this problem, i will 
>  be very thankful.
>
>1)   I have just a file path with me, an absolute path, but no dentry, 
>   no inode, no vfsmount object, which function i can call to get a 
>   "file" object associated with the absoulte file path. I have surfed 
>   arround the source code especially fs/open.c and some other files, 
>   but each function requires a parameter "mode" and "fd" beside file 
>   path. Actually, i was confuse about the "mode" parameter (and its 
>   differece with "flag"), like what to send, and secondly for "fd", i 
>   am not sure, what value to send as there is no file infact and only 
>   file path exists. Any idea?

Not sure if this is the right function, but it should get you started...

struct dentry *foooobar = lookup_one_len("/foo/bar", current->fs->root);

>2) Any functionality within linux kernel source code, to read one line 
>   per file? or some indirect way to set buffer size for one read?. 
>   That is, any existing header file for doing text I/O rather than 
>   binary within the kernel source code?

http://kernelnewbies.org/FAQ/WhyWritingFilesFromKernelIsBad
(same goes for reading)


Jan
-- 

Re: Two questions regarding Opening files within Kernel!

[Robert Hancock]

JanuGerman wrote:
> Hi Every one,
> 
>   I have got two questions regarding opening files within the Linux kernel. If some body can help me, in sorting out this problem, i will be very thankful.

First off, likely not something you should be doing:

http://kernelnewbies.org/FAQ/WhyWritingFilesFromKernelIsBad

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Re: Two questions regarding Opening files within Kernel!

[JanuGerman]

Thanks Jan for the response.


>struct dentry *foooobar = lookup_one_len("/foo/bar", current->fs->root);


But that gives me a dentry, where as file object is still not reachable. 

Question: I am currently using a function called fs.h/dentry_open which takes a "dentry", "vfsmount" object  and flag (usually RW i.e. 2), and gives me the file object. with  your suggested method, vfsmount is still not available. In this regard, any idea about a function, which gives directly the file object instead of dentry will be highly appreciated. 


OR,  (Kindly see the code below), i need some thing for "missing vfsmount".


    struct dentry *foooobar = lookup_one_len("/foo/bar", current->fs->root);
    struct file *file1 = dentry_open(foooobar, "missing vfsmount here",2)



Thanks,
JG


	
	
		
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Re: Two questions regarding Opening files within Kernel!

[Jan Engelhardt]

On Apr 7 2007 16:57, JanuGerman wrote:
>
>Thanks Jan for the response.
>
>>struct dentry *foooobar = lookup_one_len("/foo/bar", current->fs->root);
>
>But that gives me a dentry, where as file object is still not reachable.

So use filp_open.

>Question: I am currently using a function called fs.h/dentry_open which takes
>a "dentry", "vfsmount" object and flag (usually RW i.e. 2), and gives me the
>file object. with your suggested method, vfsmount is still not available. In
>this regard, any idea about a function, which gives directly the file object
>instead of dentry will be highly appreciated.
>
>
>OR,  (Kindly see the code below), i need some thing for "missing vfsmount".
>
>
>    struct dentry *foooobar = lookup_one_len("/foo/bar", current->fs->root);
>    struct file *file1 = dentry_open(foooobar, "missing vfsmount here",2)
>
>
>
>Thanks,
>JG
>
>
>	
>	
>		
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>

Jan
--