From: cranium2003 <cranium2003@yahoo.com>
To: kernel newbies <kernelnewbies@nl.linux.org>,
kernerl mail <linux-kernel@vger.kernel.org>
Subject: strace on cat /proc/my_file gives results by calling read twice why?
Date: Fri, 4 Mar 2005 23:04:21 -0800 (PST) [thread overview]
Message-ID: <20050305070421.12802.qmail@web41401.mail.yahoo.com> (raw)
hello,
I have a /proc file kernel module with its proc
read function as
static char mybuf[1024];
ssize_t my_file_read(struct file *filp, char *buf,
size_t count, loff_t *ppos)
{
printk("Reading a from a /proc file....\n");
static int b_read = 0;
int len = strlen(mybuf);
if (len == 0 || b_read) {
b_read = 0;
return 0;
}
if (len > count - 1)
len = count - 1;
copy_to_user(buf, mybuf, len);
put_user(0, &buf[len]);
++len;
b_read = 1;
return len;
}
when i strace cat /proc/my_file i found message
printing twice
Reading a from a /proc file....
Reading a from a /proc file....
Why that happening?
Also i check by writing to it as cat >
/proc/my_file
and got single result for write function call not
twice as for read.
regards,
cranium
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next reply other threads:[~2005-03-05 7:04 UTC|newest]
Thread overview: 2+ messages / expand[flat|nested] mbox.gz Atom feed top
2005-03-05 7:04 cranium2003 [this message]
[not found] <no.id>
2005-03-05 7:43 ` strace on cat /proc/my_file gives results by calling read twice why? Alan Curry
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