Gitweb:
http://git.kernel.org/git/?p=linux/kernel/git/torvalds/linux-2.6.git;a=commit;h=f528e7ba28492e363a64c80c414ded4cadf48f89
Commit: f528e7ba28492e363a64c80c414ded4cadf48f89
Parent: a5ba7971045a90a36cef8f7d5a3075600b475b74
Author: Tim Hockin <[EMAIL PROTECTED]>
AuthorDate: Sat Jul 21 17:10:35 2007 +0200
Committer: Linus Torvalds <[EMAIL PROTECTED]>
CommitDate: Sat Jul 21 18:37:10 2007 -0700
x86_64: O_EXCL on /dev/mcelog
Background:
/dev/mcelog is a clear-on-read interface. It is currently possible for
multiple users to open and read() the device. Users are protected from
each other during any one read, but not across reads.
Description:
This patch adds support for O_EXCL to /dev/mcelog. If a user opens the
device with O_EXCL, no other user may open the device (EBUSY). Likewise,
any user that tries to open the device with O_EXCL while another user has
the device will fail (EBUSY).
Result:
Applications can get exclusive access to /dev/mcelog. Applications that
do not care will be unchanged.
Alternatives:
A simpler choice would be to only allow one open() at all, regardless of
O_EXCL.
Testing:
I wrote an application that opens /dev/mcelog with O_EXCL and observed
that any other app that tried to open /dev/mcelog would fail until the
exclusive app had closed the device.
Caveats:
None.
Signed-off-by: Tim Hockin <[EMAIL PROTECTED]>
Signed-off-by: Andrew Morton <[EMAIL PROTECTED]>
Signed-off-by: Andi Kleen <[EMAIL PROTECTED]>
Signed-off-by: Linus Torvalds <[EMAIL PROTECTED]>
---
arch/x86_64/kernel/mce.c | 36 ++++++++++++++++++++++++++++++++++++
1 files changed, 36 insertions(+), 0 deletions(-)
diff --git a/arch/x86_64/kernel/mce.c b/arch/x86_64/kernel/mce.c
index f3fb817..77fee48 100644
--- a/arch/x86_64/kernel/mce.c
+++ b/arch/x86_64/kernel/mce.c
@@ -465,6 +465,40 @@ void __cpuinit mcheck_init(struct cpuinfo_x86 *c)
* Character device to read and clear the MCE log.
*/
+static DEFINE_SPINLOCK(mce_state_lock);
+static int open_count; /* #times opened */
+static int open_exclu; /* already open exclusive? */
+
+static int mce_open(struct inode *inode, struct file *file)
+{
+ spin_lock(&mce_state_lock);
+
+ if (open_exclu || (open_count && (file->f_flags & O_EXCL))) {
+ spin_unlock(&mce_state_lock);
+ return -EBUSY;
+ }
+
+ if (file->f_flags & O_EXCL)
+ open_exclu = 1;
+ open_count++;
+
+ spin_unlock(&mce_state_lock);
+
+ return 0;
+}
+
+static int mce_release(struct inode *inode, struct file *file)
+{
+ spin_lock(&mce_state_lock);
+
+ open_count--;
+ open_exclu = 0;
+
+ spin_unlock(&mce_state_lock);
+
+ return 0;
+}
+
static void collect_tscs(void *data)
{
unsigned long *cpu_tsc = (unsigned long *)data;
@@ -555,6 +589,8 @@ static int mce_ioctl(struct inode *i, struct file
*f,unsigned int cmd, unsigned
}
static const struct file_operations mce_chrdev_ops = {
+ .open = mce_open,
+ .release = mce_release,
.read = mce_read,
.ioctl = mce_ioctl,
};
-
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