* /sys inconsistent newline requirement on write
@ 2016-04-04 17:06 Steve Kenton
0 siblings, 0 replies; only message in thread
From: Steve Kenton @ 2016-04-04 17:06 UTC (permalink / raw)
To: linux-kernel
Feature or bug?
Using shell echo to write to /sys files normally adds an implicit
newline but
write() in a C program must add it explicitly. Some but not all /sys files
require a newline or the write fails. 'Extra' new lines from echo are
silently ignored and do not cause errors.
For example:
writing "1" to /sys/block/sd*/device/delete does not require a trailing
newline
writing "offline" to /sys/block/sd*/device/state does require a
trailing newline
$ make test
$ sudo ./test
write failed without newline: Invalid argument
===================================================
// Test program to illustrate required newline for writes to
/sys/block/sd*/device/state
#include <stdio.h>
#include <fcntl.h>
int main(int argc, char **argv)
{
int sysfd;
if ((sysfd = open("/sys/block/sdb/device/state", O_WRONLY)) < 0)
perror("open failed");
else
{
if (write(sysfd, "offline", 7) < 0)
perror("write failed without newline");
if (write(sysfd, "offline\n", 8) < 0)
perror("write failed with newline");
if (close(sysfd))
perror("close failed");
}
return 0;
}
^ permalink raw reply [flat|nested] only message in thread
only message in thread, other threads:[~2016-04-04 17:40 UTC | newest]
Thread overview: (only message) (download: mbox.gz / follow: Atom feed)
-- links below jump to the message on this page --
2016-04-04 17:06 /sys inconsistent newline requirement on write Steve Kenton
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).