<p dir="ltr"><br>
On 12 Jul 2015 22:20, "Amir Hezarkhani" <<a href="mailto:amir6723@gmail.com">amir6723@gmail.com</a>> wrote:<br>
><br>
> Thank for replies. About copy_to_user and copy_from_user, whats the better way? <br>
> I dont have much experience in kernel development but I'm trying to learn. Can you recommend me some books, documents, etc so I can learn more about filesystems in kernel. I am also interested to learn how mmap works because I have problems with execution of binary files in my encrypted filesystem.<br>
><br>
> On Jul 12, 2015 8:30 PM, <<a href="mailto:kernelnewbies-request@kernelnewbies.org">kernelnewbies-request@kernelnewbies.org</a>> wrote:<br>
>><br>
>><br>
>><br>
>> On Sun, Jul 12, 2015 at 8:08 PM, Freeman Zhang <<a href="mailto:freeman.zhang1992@gmail.com">freeman.zhang1992@gmail.com</a>> wrote:<br>
>>><br>
>>> -------- Original Message --------<br>
>>> > hello<br>
>>> > I am working on adding a simple encryption to file contents in ext4 driver<br>
>>> > (for learning purposes) I added simple XOR encryption to aio_read and<br>
>>> > aio_write functions and it worked until I faced this problem:<br>
>>> ><br>
>>> > when I open a file in encrypted filesystem using VIM text editor and when I<br>
>>> > try to save it it gives me this error:<br>
>>> ><br>
>>> >>> pointer block id wrong<br>
>>> >>> can not find line 1<br>
>>> ><br>
>>> > and it just corrupts the entire file!<br>
>>> ><br>
>>> > this is my aio_write function:<br>
>>> ><br>
>>> > aio_write_enc(struct kiocb *iocb, const struct iovec *iov,<br>
>>> > unsigned long nr_segs, loff_t pos)<br>
>>> > {<br>
>>> > size_t i;<br>
>>> > ssize_t ret;<br>
>>> > char *data=vmalloc(sizeof(char)*iov->iov_len);<br>
>>> > copy_from_user(data,iov->iov_base,iov->iov_len);<br>
>>> ><br>
>>> > for(i=0;i<iov->iov_len;i++)<br>
>>> > {<br>
>>> > data[i]^=5;<br>
>>> > }<br>
>>> > struct iovec iov_enc= { .iov_base = iov->iov_base, .iov_len =<br>
>>> > iov->iov_len };<br>
>>> ><br>
>>> > copy_to_user(iov_enc.iov_base,data,iov->iov_len);<br>
>>> > ret=ext4_file_write(iocb,&iov_enc,nr_segs,pos);<br>
>>> > vfree(data);<br>
>>> > return ret;<br>
>>> > }<br>
>>> ><br>
>>> > this just changes the data and then calls original function.<br>
>>> ><br>
>>> > is there anything wrong with this function? can anyone help me?<br>
>>> ><br>
>>> ><br>
>>> ><br>
>>> Hi Amir,<br>
>>><br>
>>> I'm not quite sure about what's wrong with your function, but here are<br>
>>> two suggestions I got from the list when I did similar things:<br>
>>><br>
>>> 1. wrapfs<br>
>>> 2. ecryptfs<br>
>>><br>
>>> I think you should check these two stackable filesystems if you haven't.<br>
>>><br>
>>> Hope this can help a little bit!<br>
>>><br>
>>> Freeman<br>
>>><br>
>>><br>
>>> _______________________________________________<br>
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>>><br>
>><br>
>> Hi Amir,<br>
>><br>
>> I agree with Freeman Zhang over here. The way you are doing it is not right. There is a mechanism to create stacks of file system and you should go down that path.<br>
>><br>
>> Having said this, you should definitely debug the issue that you are facing. Some pointers : -<br>
>> 1. As you have already mentioned that this is happening only for vim and not while regular read(using cat, etc), you need to check what vim does special to read a file. I would suggest make use of strace and do reading with and without vim, maybe you will get something of interest.<br>
>> 2. re-read code to check, you might be messing up while write or read.<br>
>><br>
>> Apart from these some basic practices you need to follow is : -<br>
>><br>
>> 1. check for error conditions, like you missed checking error from vmalloc() and the below code will execute even if it failed, this should be avoided.<br>
>> 2. copy_from_user & again copying back to user is in-efficient.<br>
>><br>
>><br>
>> Enjoy life,<br>
>> Rohan<br>
><br>
><br>
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></p>
<p dir="ltr">Hi Amir,</p>
<p dir="ltr">Please reply at the bottom. Regarding what's the better way would depend on how you design stuff.</p>
<p dir="ltr">Following is my recommendation :-</p>
<p dir="ltr">For conceptual knowledge of general file systems the best would be OS book by Prof Remzi Arpaci-Dusseau.<br>
Excellently explained.</p>
<p dir="ltr">For linux kernel conceptual stuff get hold of Robert love Linux kernel development.</p>
<p dir="ltr">Read lots of kernel generic filesystem code in FS dir. Lots of basic functionality is implemented in helper functions present in this dir.</p>
<p dir="ltr">Enjoy life,<br>
Rohan</p>