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POopen file O_NONBLOCKING gets lost in kernel module
 

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  1. POopen file O_NONBLOCKING gets lost in kernel module
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    <p>I am opening a file in my C program:</p> <pre><code>pcm-&gt;dfd = open(fname, O_RDONLY|O_NONBLOCK); </code></pre> <p>and later call <code>select()</code> and <code>read()</code> on it.</p> <p>But my problem is, that the <code>O_NONBLOCK</code> gets lost somewere:</p> <pre><code>ssize_t my_read(struct file *filp, char __user *user_buffer, size_t bytes_requested, loff_t *capture_ptr) { if (filp-&gt;f_flags &amp; O_NONBLOCK){ LOGI("mode: O_NONBLOCK"); } else{ LOGI("mode: BLOCKING"); // &lt;-- this is printed } .. } </code></pre> <p>I also tried</p> <pre><code>pcm-&gt;dfd=open(fname, O_RDONLY|O_NONBLOCK); // O_NONBLOCK does not work :/ int flags = fcntl(pcm-&gt;dfd, F_GETFL, 0); fcntl(pcm-&gt;dfd, F_SETFL, flags | O_NONBLOCK); </code></pre> <p>It's not a logging-problem, the driver also behaves as in blocking-mode.</p> <p>Anyone an idea?</p> <p>EDIT:</p> <p>The code which reads from the opened file is absolutely simple:</p> <pre><code>size=read(pcm-&gt;dfd,inBuffer,inBufferBytes); </code></pre> <p>I also checked the program if there's a <code>fcntl()</code> somewere else, but no..</p> <p>EDIT 2:</p> <p>May it be possible, that the <code>O_NONBLOCK</code> has an other value in my user-program (Android NDK) than in the kernel? I searched for <code>O_NONBLOCK</code> in the kernel-headers and already there are 2 different definitions.</p> <p>I also checked the <code>open</code>-implementation in my kernel module and already there <code>filp-&gt;f_flags</code> is <strong>not</strong> <code>O_NONBLOCK</code>.</p>
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    1. USMartin L.
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    1. COShow us the code performing the `read`.
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      1. UScnicutar
    2. COAdded the `read`-line.
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      1. USMartin L.
    3. COOpening files with `O_NONBLOCK` results in UB (a.k.a. _unspecified behaviour_) as per [the specs](http://pubs.opengroup.org/onlinepubs/000095399/functions/open.html).
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      1. USHristo Iliev
 

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