changing file size at run time in linux kernel code
 

how to modify the size field of file during their creation and where to do it in kernel code??

Do you mean that you want all files to be created with some non-zero size? This would very likely break a lot of programs. Why do you think this is a good idea? I sense that you are trying to use the wrong solution to a problem. Why don't you tell us what you are really trying to accomplish?

--- rod.

Why do you want to create a file in kernel space? In user space, it is very easy even if non-zero size file.

my actual problem is:-

i want to encrypt files during their creation and decrypt files during their read operation using AES algorithm, i have also written code in vfs_write() and vfs_read() for encryption and decryption respectively and also it is working nicely, but the only problem now is that k whenever i pass a file to vfs_write() whose length is not multiple of 16 (AES BLOCK SIZE) den AES does padding to it to make it a multiple of 16 and bcz of this the size of the file increases but the write() function does not know about this and so it rejects

e.g.:- suppose i enter data as "123", here length is 4 (3 length of data + 1 '\0' character) and so AES padds 12 bytes to it to make it 16 bytes (as AES works on 16 bytes blocks), but write() only takes original length which was 4 and so i want to know how to change the file size to 16 (in this case) and also where to do it in kernel code

i tried this

inode->i_size=new_length;
inode->i_op->truncate(inode);

but this is not working bcz kernel hangs and also i am not understanding where to do such things i.e., in which function and how

also i tried changing the count variable with new length in vfs_write() but then it gives error as "cat write error: No space left on device"

it works fine when i pass file which is a multiple of 16

if anyone know anything about this plz plz help me and if you could suggest me anything it's most welcome....thankyou.....

You can reference ecryptfs file system's code. It should have reference code.