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From: Greg KH <greg@kroah.com>
To: Mohana Datta Yelugoti <ymdatta.work@gmail.com>
Cc: kernelnewbies@kernelnewbies.org
Subject: Re: Doubt on show() function of sysfs attribute
Date: Wed, 27 Jan 2021 09:10:20 +0100	[thread overview]
Message-ID: <YBEf7EYr3t/cFvEt@kroah.com> (raw)
In-Reply-To: <98fe87f5-19ac-dfa7-41eb-2e00d7415021@gmail.com>

On Tue, Jan 26, 2021 at 11:07:24PM +0530, Mohana Datta Yelugoti wrote:
> Hello everyone,
> 
> I am going through Documentation/filesystems/sysfs.rst.
> 
> It says that sysfs allocates a buffer of size PAGE_SIZE and
> passes it to the show/store functions of the attribute. On
> read(), the show() method should fill the entire buffer[0].

No, that's not the case.  Please only fill in what you need sent back to
userspace and return the number of bytes you used.  A simple call to
sprintf() or better yet, sysfs_emit(), as a return statement is all you
need to do.

See the thousands of examples in the kernel of this if you need proof :)

thanks,

greg k-h

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  parent reply	other threads:[~2021-01-27  8:10 UTC|newest]

Thread overview: 5+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-01-26 17:37 Doubt on show() function of sysfs attribute Mohana Datta Yelugoti
2021-01-27  3:51 ` Valdis Klētnieks
2021-01-27  8:10 ` Greg KH [this message]
2021-01-27  9:39   ` Lukas Bulwahn
2021-01-27 16:21   ` Mohana Datta Yelugoti

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