Re: [Qemu-devel] About the snapshot
On Tue, Dec 6, 2011 at 9:07 AM, Zhi Hui Li zhihu...@linux.vnet.ibm.com wrote: 1) : for example: BDRVQcowState *s = bs-opaque; s-snapshots s-nb_snapshots 1:use the command: qemu-img snapshot ./test.qcow2 -c aa the memory of the s-snapshot don't free, if the s-nb_snapshots is large, Does it have some problems. 2: use the command: qemu-system-x86_64 ./test.qcow2 -snapshot when the program ends, Does it need to free the s-snapshots ? These two commands are unrelated. QEMU uses the term snapshot for several different features: 1. qemu-img snapshot refers to internal snapshots that are contained within qcow2 image files. The savevm/loadvm/delvm monitor commands operate on internal snapshots. 2. qemu -snapshot refers to a temporary qcow2 image file created to buffer any data that the guest writes. When QEMU exits your disk image is not modified and the temporary qcow2 file is deleted. You can also apply the buffer to the disk image using the commit monitor command. 2): in the function of qcow2_update_snapshot_refcount it has some goto fail ; if the function runs some times, then something makes it goto fail, I am not sure whether it will make the refcount incorrect. When an error occurs its possible that refcount leaks are introduced (the refcount was increment but will never be used), but we should never decrement a reference that is still in use. Please be more specific about the problem so that Kevin or I can take a look. Stefan
Re: [Qemu-devel] About the snapshot
On 2011年12月06日 17:40, Stefan Hajnoczi wrote: On Tue, Dec 6, 2011 at 9:07 AM, Zhi Hui Lizhihu...@linux.vnet.ibm.com wrote: 1) : for example: BDRVQcowState *s = bs-opaque; s-snapshots s-nb_snapshots 1:use the command: qemu-img snapshot ./test.qcow2 -c aa the memory of the s-snapshot don't free, if the s-nb_snapshots is large, Does it have some problems. 2: use the command: qemu-system-x86_64 ./test.qcow2 -snapshot when the program ends, Does it need to free the s-snapshots ? These two commands are unrelated. QEMU uses the term snapshot for several different features: 1. qemu-img snapshot refers to internal snapshots that are contained within qcow2 image files. The savevm/loadvm/delvm monitor commands operate on internal snapshots. 2. qemu -snapshot refers to a temporary qcow2 image file created to buffer any data that the guest writes. When QEMU exits your disk image is not modified and the temporary qcow2 file is deleted. You can also apply the buffer to the disk image using the commit monitor command. yes, I understand what you say, but the qemu-img and savevm both call the function of qcow2_snapshot_create, when I use the command qemu-img snapshot ./test.qcow2 -c aa, but the memory of the s-snapshot don't free. 2): in the function of qcow2_update_snapshot_refcount it has some goto fail ; if the function runs some times, then something makes it goto fail, I am not sure whether it will make the refcount incorrect. When an error occurs its possible that refcount leaks are introduced (the refcount was increment but will never be used), but we should never decrement a reference that is still in use. Please be more specific about the problem so that Kevin or I can take a look. Stefan Ok, I got it. thank you very much !
Re: [Qemu-devel] About the snapshot
On Tue, Dec 6, 2011 at 10:01 AM, Zhi Hui Li zhihu...@linux.vnet.ibm.com wrote: On 2011年12月06日 17:40, Stefan Hajnoczi wrote: On Tue, Dec 6, 2011 at 9:07 AM, Zhi Hui Lizhihu...@linux.vnet.ibm.com wrote: 1) : for example: BDRVQcowState *s = bs-opaque; s-snapshots s-nb_snapshots 1:use the command: qemu-img snapshot ./test.qcow2 -c aa the memory of the s-snapshot don't free, if the s-nb_snapshots is large, Does it have some problems. 2: use the command: qemu-system-x86_64 ./test.qcow2 -snapshot when the program ends, Does it need to free the s-snapshots ? These two commands are unrelated. QEMU uses the term snapshot for several different features: 1. qemu-img snapshot refers to internal snapshots that are contained within qcow2 image files. The savevm/loadvm/delvm monitor commands operate on internal snapshots. 2. qemu -snapshot refers to a temporary qcow2 image file created to buffer any data that the guest writes. When QEMU exits your disk image is not modified and the temporary qcow2 file is deleted. You can also apply the buffer to the disk image using the commit monitor command. yes, I understand what you say, but the qemu-img and savevm both call the function of qcow2_snapshot_create, when I use the command qemu-img snapshot ./test.qcow2 -c aa, but the memory of the s-snapshot don't free. Okay, I think you're saying that in #1 s-snapshots is leaked because qcow2_free_snapshots() is not being called from qcow2_close(). Do you want to send a patch to fix this? Stefan
Re: [Qemu-devel] About the snapshot
2011/12/6 Stefan Hajnoczi stefa...@gmail.com On Tue, Dec 6, 2011 at 10:01 AM, Zhi Hui Li zhihu...@linux.vnet.ibm.com wrote: On 2011年12月06日 17:40, Stefan Hajnoczi wrote: On Tue, Dec 6, 2011 at 9:07 AM, Zhi Hui Lizhihu...@linux.vnet.ibm.com wrote: 1) : for example: BDRVQcowState *s = bs-opaque; s-snapshots s-nb_snapshots 1:use the command: qemu-img snapshot ./test.qcow2 -c aa the memory of the s-snapshot don't free, if the s-nb_snapshots is large, Does it have some problems. 2: use the command: qemu-system-x86_64 ./test.qcow2 -snapshot when the program ends, Does it need to free the s-snapshots ? Okay, I think you're saying that in #1 s-snapshots is leaked because qcow2_free_snapshots() is not being called from qcow2_close(). Do you want to send a patch to fix this? Ok, I will send a patch tomorrow. But I think in the #2 it also need to call qcow2_free_snapshots() , if you have called several times savevm, the s-snapshots will very large, when the process end, it also need to free. Thank you very much for your feedback ! Stefan
Re: [Qemu-devel] About the snapshot
2011/12/6 Zhi Hui Li zhihu...@linux.vnet.ibm.com: 2011/12/6 Stefan Hajnoczi stefa...@gmail.com On Tue, Dec 6, 2011 at 10:01 AM, Zhi Hui Li zhihu...@linux.vnet.ibm.com wrote: On 2011年12月06日 17:40, Stefan Hajnoczi wrote: On Tue, Dec 6, 2011 at 9:07 AM, Zhi Hui Lizhihu...@linux.vnet.ibm.com wrote: 1) : for example: BDRVQcowState *s = bs-opaque; s-snapshots s-nb_snapshots 1:use the command: qemu-img snapshot ./test.qcow2 -c aa the memory of the s-snapshot don't free, if the s-nb_snapshots is large, Does it have some problems. 2: use the command: qemu-system-x86_64 ./test.qcow2 -snapshot when the program ends, Does it need to free the s-snapshots ? Okay, I think you're saying that in #1 s-snapshots is leaked because qcow2_free_snapshots() is not being called from qcow2_close(). Do you want to send a patch to fix this? Ok, I will send a patch tomorrow. But I think in the #2 it also need to call qcow2_free_snapshots() , if you have called several times savevm, the s-snapshots will very large, when the process end, it also need to free. Right, I think I understand what you're saying. I was thinking about what #1 and #2 mean differently, but it doesn't matter. If qcow2_close() frees s-snapshots then the problem is solved in all possible qcow2 use cases, including #2 with savevm. Stefan
