Bug 1138691

Fix included in qemu-kvm-1.5.3-79.el7

Verify this issue with the same steps as Chao Yang.

#######qemu-kvm-1.5.3-79.el7.x86_64:
host info:
# uname -r && rpm -q qemu-kvm
3.10.0-205.el7.x86_64
qemu-kvm-1.5.3-79.el7.x86_64

Scenario 1:
-----------
# sync; echo 3 > /proc/sys/vm/drop_caches
# free -m;qemu-img convert -t none -f raw -O qcow2 image-1.raw image-test.qcow2; free -m
              total        used        free      shared  buff/cache   available
Mem:           7781         290        7367           8     ***124***     7318
Swap:          8063          73        7990
              total        used        free      shared  buff/cache   available
Mem:           7781         290        2509           8     ***4981***     7253
Swap:          8063          73        7990

# sync; echo 3 > /proc/sys/vm/drop_caches
# free -m;qemu-img convert -t none -f raw -O qcow2 image-1.raw image-test.qcow2 -T none; free -m
              total        used        free      shared  buff/cache   available
Mem:           7781         290        7367           8      ***124***     7318
Swap:          8063          73        7990
              total        used        free      shared  buff/cache   available
Mem:           7781         291        7362           8      ***128***     7316
Swap:          8063          73        7990

As we can see above, cached column differs a lot from without '-T none' and with '-T none'.

Scenario 2:
-----------
If you call "strace -e trace=open qemu-img xxx -T none source.img destination.img", the last time each file (source.img and destination.img) is opened with the ***O_DIRECT*** flag.

2.1 qemu-img convert.
# git diff convert-without-T.log convert-with-T.log 
diff --git a/convert-without-T.log b/convert-with-T.log
index 5475bc7..dc75a8b 100644
--- a/convert-without-T.log
+++ b/convert-with-T.log
@@ -19,7 +19,7 @@ open("/lib64/libcrypto.so.10", O_RDONLY|O_CLOEXEC) = 3
 open("/lib64/libgpg-error.so.0", O_RDONLY|O_CLOEXEC) = 3
 open("image-1.raw", O_RDONLY|O_NONBLOCK|O_CLOEXEC) = 6
 open("image-1.raw", O_RDONLY|O_NONBLOCK|O_CLOEXEC) = 6
-open("image-1.raw", O_RDONLY|O_CLOEXEC) = 6
+open("image-1.raw", O_RDONLY|***O_DIRECT***|O_CLOEXEC) = 6
 open("image-1.qcow2", O_RDONLY|O_NONBLOCK|O_CLOEXEC) = 7
 open("image-1.qcow2", O_RDONLY|O_NONBLOCK|O_CLOEXEC) = 7
 open("image-1.qcow2", O_RDONLY|O_NONBLOCK|O_CLOEXEC) = 7

2.2 qemu-img check.
# git diff check-without-T.log check-with-T.log 
diff --git a/check-without-T.log b/check-with-T.log
index d9a737a..b1e5f18 100644
--- a/check-without-T.log
+++ b/check-with-T.log
@@ -19,5 +19,5 @@ open("/lib64/libcrypto.so.10", O_RDONLY|O_CLOEXEC) = 3
 open("/lib64/libgpg-error.so.0", O_RDONLY|O_CLOEXEC) = 3
 open("image-1.qcow2", O_RDONLY|O_NONBLOCK|O_CLOEXEC) = 6
 open("image-1.qcow2", O_RDONLY|O_NONBLOCK|O_CLOEXEC) = 6
-open("image-1.qcow2", O_RDONLY|O_CLOEXEC) = 6
+open("image-1.qcow2", O_RDONLY|***O_DIRECT***|O_CLOEXEC) = 6
 +++ exited with 0 +++

2.3 qemu-img compare.
# git diff compare-without-T.log compare-with-T.log 
diff --git a/compare-without-T.log b/compare-with-T.log
index 646175e..afc45cc 100644
--- a/compare-without-T.log
+++ b/compare-with-T.log
@@ -19,8 +19,8 @@ open("/lib64/libcrypto.so.10", O_RDONLY|O_CLOEXEC) = 3
 open("/lib64/libgpg-error.so.0", O_RDONLY|O_CLOEXEC) = 3
 open("image-1.raw", O_RDONLY|O_NONBLOCK|O_CLOEXEC) = 6
 open("image-1.raw", O_RDONLY|O_NONBLOCK|O_CLOEXEC) = 6
-open("image-1.raw", O_RDONLY|O_CLOEXEC) = 6
+open("image-1.raw", O_RDONLY|***O_DIRECT***|O_CLOEXEC) = 6
 open("image-1.qcow2", O_RDONLY|O_NONBLOCK|O_CLOEXEC) = 7
 open("image-1.qcow2", O_RDONLY|O_NONBLOCK|O_CLOEXEC) = 7
-open("image-1.qcow2", O_RDONLY|O_CLOEXEC) = 7
+open("image-1.qcow2", O_RDONLY|***O_DIRECT***|O_CLOEXEC) = 7
 +++ exited with 0 +++

2.4 qemu-img rebase.
# git diff rebase-without-T.log rebase-with-T.log 
diff --git a/rebase-without-T.log b/rebase-with-T.log
index 451ae2c..0fbd0ec 100644
--- a/rebase-without-T.log
+++ b/rebase-with-T.log
@@ -25,8 +25,8 @@ open("image-1.qcow2", O_RDONLY|O_NONBLOCK|O_CLOEXEC) = 8
 open("image-1.qcow2", O_RDONLY|O_DIRECT|O_CLOEXEC) = 8
 open("image-1.qcow2", O_RDONLY|O_NONBLOCK|O_CLOEXEC) = 9
 open("image-1.qcow2", O_RDONLY|O_NONBLOCK|O_CLOEXEC) = 9
-open("image-1.qcow2", O_RDONLY|O_CLOEXEC) = 9
+open("image-1.qcow2", O_RDONLY|***O_DIRECT***|O_CLOEXEC) = 9
 open("image-1.qcow2", O_RDONLY|O_NONBLOCK|O_CLOEXEC) = 10
 open("image-1.qcow2", O_RDONLY|O_NONBLOCK|O_CLOEXEC) = 10
-open("image-1.qcow2", O_RDONLY|O_CLOEXEC) = 10
+open("image-1.qcow2", O_RDONLY|***O_DIRECT***|O_CLOEXEC) = 10
 +++ exited with 0 +++

2.5 qemu-img amend.
qemu-img amend fail to specify the cache mode to bypass the host cache in qemu-kvm-1.5.3-x verison(separated it to new bug 1166476 to trace it).


#######qemu-kvm-rhev-2.1.2-8.el7.x86_64:
host info:
# uname -r && rpm -q qemu-kvm-rhev
3.10.0-205.el7.x86_64
qemu-kvm-rhev-2.1.2-8.el7.x86_64

Scenario 1:
-----------
# sync; echo 3 > /proc/sys/vm/drop_caches
# free -m;qemu-img convert -t none -f raw -O qcow2 image-1.raw image-test.qcow2; free -m

# sync; echo 3 > /proc/sys/vm/drop_caches
# free -m;qemu-img convert -t none -f raw -O qcow2 image-1.raw image-test.qcow2 -T none; free -m

Scenario 2:
-----------
2.1 qemu-img convert.
2.2 qemu-img check.
2.3 qemu-img compare.
2.4 qemu-img rebase.
2.5 qemu-img amend.

It fail to work with qemu-kvm-rhev-2.1.2-X version which i have separated it to new bug 1166481 to trace it.

Bug 1166481 - Allow qemu-img to bypass the host cache (check, compare, convert, rebase, amend)

Base on above, this issue has been fixed, new issues have been separated to new bug to trace it. Move this issue to VERIFIED status first, thanks.

Best Regards,
sluo

Since the problem described in this bug report should be
resolved in a recent advisory, it has been closed with a
resolution of ERRATA.

For information on the advisory, and where to find the updated
files, follow the link below.

If the solution does not work for you, open a new bug report.

https://rhn.redhat.com/errata/RHSA-2015-0349.html