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Re: [PATCH] exec: fetch the alignment of Linux devdax pmem character dev
From: |
Joao Martins |
Subject: |
Re: [PATCH] exec: fetch the alignment of Linux devdax pmem character device nodes |
Date: |
Tue, 7 Apr 2020 19:28:33 +0100 |
On 4/7/20 5:55 PM, Dan Williams wrote:
> On Tue, Apr 7, 2020 at 4:01 AM Joao Martins <address@hidden> wrote:
>> On 4/1/20 4:13 AM, Jingqi Liu wrote:
>>> If the backend file is devdax pmem character device, the alignment
>>> specified by the option 'align=NUM' in the '-object memory-backend-file'
>>> needs to match the alignment requirement of the devdax pmem character
>>> device.
>>>
>>> This patch fetches the devdax pmem file 'align', so that we can compare
>>> it with the NUM of 'align=NUM'.
>>> The NUM needs to be larger than or equal to the devdax pmem file 'align'.
>>>
>>> It also fixes the problem that mmap() returns failure in qemu_ram_mmap()
>>> when the NUM of 'align=NUM' is less than the devdax pmem file 'align'.
>>>
>>> Cc: Dan Williams <address@hidden>
>>> Signed-off-by: Jingqi Liu <address@hidden>
>>> ---
>>> exec.c | 46 +++++++++++++++++++++++++++++++++++++++++++++-
>>> 1 file changed, 45 insertions(+), 1 deletion(-)
>>>
>>> diff --git a/exec.c b/exec.c
>>> index de9d949902..8221abffec 100644
>>> --- a/exec.c
>>> +++ b/exec.c
>>> @@ -1736,6 +1736,42 @@ static int64_t get_file_size(int fd)
>>> return size;
>>> }
>>>
>>> +static int64_t get_file_align(int fd)
>>> +{
>>> + int64_t align = -1;
>>> +#if defined(__linux__)
>>> + struct stat st;
>>> +
>>> + if (fstat(fd, &st) < 0) {
>>> + return -errno;
>>> + }
>>> +
>>> + /* Special handling for devdax character devices */
>>> + if (S_ISCHR(st.st_mode)) {
>>> + g_autofree char *subsystem_path = NULL;
>>> + g_autofree char *subsystem = NULL;
>>> +
>>> + subsystem_path = g_strdup_printf("/sys/dev/char/%d:%d/subsystem",
>>> + major(st.st_rdev),
>>> minor(st.st_rdev));
>>> + subsystem = g_file_read_link(subsystem_path, NULL);
>>> +
>>> + if (subsystem && g_str_has_suffix(subsystem, "/dax")) {
>>> + g_autofree char *align_path = NULL;
>>> + g_autofree char *align_str = NULL;
>>> +
>>> + align_path =
>>> g_strdup_printf("/sys/dev/char/%d:%d/device/align",
>>> + major(st.st_rdev), minor(st.st_rdev));
>>> +
>>
>> Perhaps, you meant instead:
>>
>> /sys/dev/char/%d:%d/align
>>
>
> Hmm, are you sure that's working?
It is, except that I made the slight mistake of testing with a bunch of wip
patches on top which one of them actually adds the 'align' to child dax device.
Argh, my apologies - and thanks for noticing.
> I expect the alignment to be found
> in the region device:
>
> /sys/class/dax:
> /sys/devices/LNXSYSTM:00/LNXSYBUS:00/ACPI0012:00/ndbus1/region1/dax1.1/dax1.0
> $(readlink -f /sys/dev/char/253\:263)/../align
> $(readlink -f /sys/dev/char/253\:263)/device/align
>
>
> /sys/bus/dax:
> /sys/devices/LNXSYSTM:00/LNXSYBUS:00/ACPI0012:00/ndbus1/region1/dax1.0/dax1.0
> $(readlink -f /sys/dev/char/253\:265)/../align
> $(readlink -f /sys/dev/char/253\:265)/device/align <-- No such file
>
> The use of the /sys/dev/char/%d:%d/device is only supported by the
> deprecated /sys/class/dax.
I don't have the deprecated dax class enabled as could you tell, so the second
case is what I was testing. Except it wasn't a namespace/nvdimm but rather an
hmem device-dax.
'../align' though covers only one case? What about hmem which '../align' returns
ENOENT; perhaps using '../dax_region/align' instead which is common to both?
Albeit that wouldn't address the sub-division devices (that I mention above)
> The current /sys/bus/dax device-model can
> be a drop in replacement as long as software is not written to the
> /sys/class sysfs layout, i.e. it uses ../ instead of device/ to walk
> to the region properties.
>
/nods
- Re: [PATCH] exec: fetch the alignment of Linux devdax pmem character device nodes, (continued)
- Re: [PATCH] exec: fetch the alignment of Linux devdax pmem character device nodes, Dan Williams, 2020/04/07
- Re: [PATCH] exec: fetch the alignment of Linux devdax pmem character device nodes,
Joao Martins <=
- Re: [PATCH] exec: fetch the alignment of Linux devdax pmem character device nodes, Paolo Bonzini, 2020/04/07
- Re: [PATCH] exec: fetch the alignment of Linux devdax pmem character device nodes, Liu, Jingqi, 2020/04/07
- Re: [PATCH] exec: fetch the alignment of Linux devdax pmem character device nodes, Joao Martins, 2020/04/08
- Re: [PATCH] exec: fetch the alignment of Linux devdax pmem character device nodes, Liu, Jingqi, 2020/04/09
- Re: [PATCH] exec: fetch the alignment of Linux devdax pmem character device nodes, Dan Williams, 2020/04/09
- Re: [PATCH] exec: fetch the alignment of Linux devdax pmem character device nodes, Paolo Bonzini, 2020/04/09
- Re: [PATCH] exec: fetch the alignment of Linux devdax pmem character device nodes, Liu, Jingqi, 2020/04/09