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MXS-1705 Try with O_DIRECT, if fails try without

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Instead of trying to figure out whether the kernel supports O_DIRECT
in conjunction with pipes, let's just use it and if it fails, try
without O_DIRECT.

Case in point, based on circumstantial evidence it seems that in a
container context, it may appear as if the kernel supports O_DIRECT
when it in reality does not. So better to use brute-force.
This commit is contained in:
Johan Wikman 2018-03-07 14:03:24 +02:00
parent e036582a98
commit bf9767e54e
1 changed files with 18 additions and 62 deletions
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80
server/core/messagequeue.cc
View File

@ -16,7 +16,6 @@
#include <fcntl.h>
#include <string.h>
#include <unistd.h>
#include <sys/utsname.h>
#include <maxscale/debug.h>
#include <maxscale/log_manager.h>
#include "internal/worker.hh"
@ -27,11 +26,9 @@ namespace
static struct
{
bool initialized;
int pipe_flags;
} this_unit =
{
false,
O_NONBLOCK | O_CLOEXEC
false
};
}
@ -67,63 +64,6 @@ bool MessageQueue::init()
{
ss_dassert(!this_unit.initialized);
/* From "man 7 pipe"
* ----
*
* O_NONBLOCK enabled, n <= PIPE_BUF
* If there is room to write n bytes to the pipe, then write(2)
* succeeds immediately, writing all n bytes; otherwise write(2)
* fails, with errno set to EAGAIN.
*
* ... (On Linux, PIPE_BUF is 4096 bytes.)
*
* ----
*
* As O_NONBLOCK is set and the messages are less than 4096 bytes,
* O_DIRECT should not be needed and we should be safe without it.
*
* However, to be in the safe side, if we run on kernel version >= 3.4
* we use it.
*/
utsname u;
if (uname(&u) == 0)
{
char* p;
char* zMajor = strtok_r(u.release, ".", &p);
char* zMinor = strtok_r(NULL, ".", &p);
if (zMajor && zMinor)
{
int major = atoi(zMajor);
int minor = atoi(zMinor);
if (major >= 3 && minor >= 4)
{
// O_DIRECT for pipes is supported from kernel 3.4 onwards.
this_unit.pipe_flags |= O_DIRECT;
}
else
{
MXS_NOTICE("O_DIRECT is not supported for pipes on Linux kernel %s "
"(supported from version 3.4 onwards), NOT using it.",
u.release);
}
}
else
{
MXS_WARNING("Syntax used in utsname.release seems to have changed, "
"not able to figure out current kernel version. Assuming "
"O_DIRECT is not supported for pipes.");
}
}
else
{
MXS_WARNING("uname() failed, assuming O_DIRECT is not supported for pipes: %s",
mxs_strerror(errno));
}
this_unit.initialized = true;
return this_unit.initialized;
@ -144,7 +84,23 @@ MessageQueue* MessageQueue::create(Handler* pHandler)
MessageQueue* pThis = NULL;
int fds[2];
if (pipe2(fds, this_unit.pipe_flags) == 0)
int rv = pipe2(fds, O_NONBLOCK | O_CLOEXEC | O_DIRECT);
if ((rv != 0) && (errno == EINVAL))
{
// Ok, apparently the kernel does not support O_DIRECT. Let's try without.
rv = pipe2(fds, O_NONBLOCK | O_CLOEXEC);
if (rv == 0)
{
// Succeeded, so apparently it was the missing support for O_DIRECT.
MXS_WARNING("Platform does not support O_DIRECT in conjunction with pipes, "
"using without.");
}
}
if (rv == 0)
{
int read_fd = fds[0];
int write_fd = fds[1];