Note: This bug is displayed in read-only format because the product is no longer active in Red Hat Bugzilla.
RHEL Engineering is moving the tracking of its product development work on RHEL 6 through RHEL 9 to Red Hat Jira (issues.redhat.com). If you're a Red Hat customer, please continue to file support cases via the Red Hat customer portal. If you're not, please head to the "RHEL project" in Red Hat Jira and file new tickets here. Individual Bugzilla bugs in the statuses "NEW", "ASSIGNED", and "POST" are being migrated throughout September 2023. Bugs of Red Hat partners with an assigned Engineering Partner Manager (EPM) are migrated in late September as per pre-agreed dates. Bugs against components "kernel", "kernel-rt", and "kpatch" are only migrated if still in "NEW" or "ASSIGNED". If you cannot log in to RH Jira, please consult article #7032570. That failing, please send an e-mail to the RH Jira admins at rh-issues@redhat.com to troubleshoot your issue as a user management inquiry. The email creates a ServiceNow ticket with Red Hat. Individual Bugzilla bugs that are migrated will be moved to status "CLOSED", resolution "MIGRATED", and set with "MigratedToJIRA" in "Keywords". The link to the successor Jira issue will be found under "Links", have a little "two-footprint" icon next to it, and direct you to the "RHEL project" in Red Hat Jira (issue links are of type "https://issues.redhat.com/browse/RHEL-XXXX", where "X" is a digit). This same link will be available in a blue banner at the top of the page informing you that that bug has been migrated.

Bug 607262

Summary: Read from /proc/xen/xenbus does not honor O_NONBLOCK
Product: Red Hat Enterprise Linux 6 Reporter: Paolo Bonzini <pbonzini>
Component: kernelAssignee: Paolo Bonzini <pbonzini>
Status: CLOSED ERRATA QA Contact: Boris Ranto <branto>
Severity: low Docs Contact:
Priority: low    
Version: 6.0CC: branto, clalance, drjones, lihuang, qcai, xen-maint
Target Milestone: rc   
Target Release: ---   
Hardware: All   
OS: Linux   
Whiteboard:
Fixed In Version: kernel-2.6.32-112.el6 Doc Type: Bug Fix
Doc Text:
Story Points: ---
Clone Of: 470801 Environment:
Last Closed: 2011-05-23 20:40:10 UTC Type: ---
Regression: --- Mount Type: ---
Documentation: --- CRM:
Verified Versions: Category: ---
oVirt Team: --- RHEL 7.3 requirements from Atomic Host:
Cloudforms Team: --- Target Upstream Version:
Embargoed:
Bug Depends On: 470801    
Bug Blocks: 523117    

Description Paolo Bonzini 2010-06-23 16:28:27 UTC 
+++ This bug was initially created as a clone of Bug #470801 +++

Description of problem:
After open(2) on /proc/xen/xenbus with O_NONBLOCK flag, read(2) on the
file is blocked, and wait for an event.

Version-Release number of selected component (if applicable):
kernel-xen-2.6.18-92.el5

How reproducible:
Always

Steps to Reproduce:
1. open ("/proc/xen/xenbus", O_RDONLY | O_NONBLOCK);
2. read (fd, buf, 4096);
  
Actual results:
read(2) is blocked.

Expected results:
read(2) shall return EAGAIN.

--- Additional comment from bburns on 2009-02-24 14:47:39 EST ---

Assigned.

--- Additional comment from pm-rhel on 2010-02-09 17:38:06 EST ---

Since the release flag was set to ? after the pm_ack flag was set
to + (was likely set for the previous release), the pm_ack flag has
been reset to ? by the bugbot (pm-rhel). This action ensures the
proper review by Product Management.
Comment 2 RHEL Program Management 2010-06-23 16:52:55 UTC 
This request was evaluated by Red Hat Product Management for inclusion in a Red
Hat Enterprise Linux major release.  Product Management has requested further
review of this request by Red Hat Engineering, for potential inclusion in a Red
Hat Enterprise Linux Major release.  This request is not yet committed for
inclusion.
Comment 3 Paolo Bonzini 2010-06-24 16:08:02 UTC 
reproducer:

#include <stdlib.h>
#include <errno.h>
#include <fcntl.h>
#include <unistd.h>
int main()
{
  char buf[256];
  int fd = open ("/proc/xen/xenbus", O_RDONLY | O_NONBLOCK); 
  if (fd == -1) {
    perror ("/proc/xen/xenbus");
    exit (1);
  }
  alarm (5);
  while (read (fd, buf, 256) == -1 && errno != EAGAIN)
    ;
  puts ("works");
  exit (0);
}
Comment 4 RHEL Program Management 2010-07-15 14:26:23 UTC 
This issue has been proposed when we are only considering blocker
issues in the current Red Hat Enterprise Linux release. It has
been denied for the current Red Hat Enterprise Linux release.

** If you would still like this issue considered for the current
release, ask your support representative to file as a blocker on
your behalf. Otherwise ask that it be considered for the next
Red Hat Enterprise Linux release. **
Comment 7 RHEL Program Management 2010-11-19 20:19:35 UTC 
This request was evaluated by Red Hat Product Management for inclusion
in a Red Hat Enterprise Linux maintenance release. Product Management has 
requested further review of this request by Red Hat Engineering, for potential
inclusion in a Red Hat Enterprise Linux Update release for currently deployed 
products. This request is not yet committed for inclusion in an Update release.
Comment 8 Paolo Bonzini 2011-01-05 10:43:20 UTC 
It's upstream commit 6280f190 (from 2.6.36).
Comment 9 Aristeu Rozanski 2011-02-03 15:39:20 UTC 
Patch(es) available on kernel-2.6.32-112.el6
Comment 13 errata-xmlrpc 2011-05-23 20:40:10 UTC 
An advisory has been issued which should help the problem
described in this bug report. This report is therefore being
closed with a resolution of ERRATA. For more information
on therefore solution and/or where to find the updated files,
please follow the link below. You may reopen this bug report
if the solution does not work for you.

http://rhn.redhat.com/errata/RHSA-2011-0542.html