mkfs.btrfs cannot find rotational file for SSD detection for a pmem device
by Elliott, Robert (Persistent Memory)
mkfs.btrfs does not detect pmem devices as being SSDs in kernel 4.2.
Label: (null)
UUID: 46603efe-728c-43fe-8241-ffc125e1a7ed
Node size: 16384
Sector size: 4096
Filesystem size: 8.00GiB
Block group profiles:
Data: single 8.00MiB
Metadata: DUP 417.56MiB
System: DUP 12.00MiB
SSD detected: no
Incompat features: extref, skinny-metadata
Number of devices: 1
Devices:
ID SIZE PATH
1 8.00GiB /dev/pmem0
mkfs.btrfs opens "/sys/block/%s/queue/rotational" and looks for
0 (non-rotational - an SSD) or non-zero (rotational - a HDD).
However, strace shows it is having trouble creating that path.
The blkid_devno_to_wholedisk function from libblkid leads it to
this path:
/sys/block/LNXSY/queue/rotational
which doesn't exist.
That is based on:
$ realpath /sys/block/pmem0
/sys/devices/LNXSYSTM:00/LNXSYBUS:00/ACPI0012:00/ndbus1/region0/namespace0.0/block/pmem0
$ realpath /sys/dev/block/259:0
/sys/devices/LNXSYSTM:00/LNXSYBUS:00/ACPI0012:00/ndbus1/region0/namespace0.0/block/pmem0
The impact looks limited to the print and causing it to not
automatically disable "metadata duplication on a single device."
References:
git://git.kernel.org/pub/scm/linux/kernel/git/mason/btrfs-progs.git
git://git.kernel.org/pub/scm/utils/util-linux/util-linux.git
http://comments.gmane.org/gmane.comp.file-systems.btrfs/18749
mkfs.c excerpt
==============
static int is_ssd(const char *file)
{
...
/* Get whole disk name (not full path) for this devno */
ret = blkid_devno_to_wholedisk(devno,
wholedisk, sizeof(wholedisk), NULL);
if (ret) {
blkid_free_probe(probe);
return 0;
}
snprintf(sysfs_path, PATH_MAX, "/sys/block/%s/queue/rotational",
wholedisk);
blkid_free_probe(probe);
fd = open(sysfs_path, O_RDONLY);
if (fd < 0) {
return 0;
}
if (read(fd, &rotational, sizeof(char)) < sizeof(char)) {
close(fd);
return 0;
...
int main(int ac, char **av)
...
if (!mixed) {
if (!metadata_profile_opt) {
if (dev_cnt == 1 && ssd && verbose)
printf("Detected a SSD, turning off metadata "
"duplication. Mkfs with -m dup if you want to "
"force metadata duplication.\n");
metadata_profile = (dev_cnt > 1) ?
BTRFS_BLOCK_GROUP_RAID1 : (ssd) ?
0: BTRFS_BLOCK_GROUP_DUP;
}
strace
======
open("/dev/pmem0", O_RDWR|O_EXCL) = 3
fstat(3, {st_mode=S_IFBLK|0660, st_rdev=makedev(259, 0), ...}) = 0
close(3) = 0
open("/dev/pmem0", O_RDONLY|O_CLOEXEC) = 3
fadvise64(3, 0, 0, POSIX_FADV_RANDOM) = 0
fstat(3, {st_mode=S_IFBLK|0660, st_rdev=makedev(259, 0), ...}) = 0
uname({sysname="Linux", nodename="s18", ...}) = 0
ioctl(3, BLKGETSIZE64, 8589934592) = 0
open("/sys/dev/block/259:0", O_RDONLY|O_CLOEXEC) = 4
openat(4, "dm/uuid", O_RDONLY|O_CLOEXEC) = -1 ENOENT (No such file or directory)
close(4) = 0
open("/sys/dev/block/259:0", O_RDONLY|O_CLOEXEC) = 4
newfstatat(4, "partition", 0x7fffb67faa50, 0) = -1 ENOENT (No such file or directory)
openat(4, "dm/uuid", O_RDONLY|O_CLOEXEC) = -1 ENOENT (No such file or directory)
close(4) = 0
ioctl(3, CDROM_GET_CAPABILITY, 0) = -1 ENOTTY (Inappropriate ioctl for device)
open("/sys/dev/block/259:0", O_RDONLY|O_CLOEXEC) = 4
newfstatat(4, "partition", 0x7fffb67fab90, 0) = -1 ENOENT (No such file or directory)
openat(4, "dm/uuid", O_RDONLY|O_CLOEXEC) = -1 ENOENT (No such file or directory)
readlink("/sys/dev/block/259:0", "../../devices/LNXSYSTM:00/LNXSY", 31) = 31
close(4) = 0
close(3) = 0
open("/sys/block/LNXSY/queue/rotational", O_RDONLY) = -1 ENOENT (No such file or directory)
open("/dev/pmem0", O_RDONLY) = 3
fstat(3, {st_mode=S_IFBLK|0660, st_rdev=makedev(259, 0), ...}) = 0
ioctl(3, BLKGETSIZE64, 8589934592) = 0
close(3) = 0
...
