From a9fd30e6332a04a8b5ba409dc738ecefa5c1b735 Mon Sep 17 00:00:00 2001 From: Chunyan Liu Date: Tue, 15 Jul 2014 16:49:46 +0800 Subject: [PATCH] storagevol: add nocow to vol xml Add 'nocow' to storage volume xml so that user can have an option to set NOCOW flag to the newly created volume. It's useful on btrfs file system to enhance performance. Btrfs has low performance when hosting VM images, even more when the guest in those VM are also using btrfs as file system. One way to mitigate this bad performance is to turn off COW attributes on VM files. Generally, there are two ways to turn off COW on btrfs: a) by mounting fs with nodatacow, then all newly created files will be NOCOW. b) per file. Add the NOCOW file attribute. It could only be done to empty or new files. This patch tries the second way, according to 'nocow' option, it could set NOCOW flag per file: for raw file images, handle 'nocow' in libvirt code; for non-raw file images, pass 'nocow=on' option to qemu-img, and let qemu-img to handle that (requires qemu-img version >= 2.1). Signed-off-by: Chunyan Liu --- docs/formatstorage.html.in | 7 +++++++ docs/schemas/storagevol.rng | 5 +++++ src/conf/storage_conf.c | 3 +++ src/storage/storage_backend.c | 22 ++++++++++++++++++++++ src/util/virstoragefile.h | 1 + 5 files changed, 38 insertions(+) diff --git a/docs/formatstorage.html.in b/docs/formatstorage.html.in index 1cd82b4565..789701c18c 100644 --- a/docs/formatstorage.html.in +++ b/docs/formatstorage.html.in @@ -385,6 +385,7 @@ <label>virt_image_t</label> </permissions> <compat>1.1</compat> + <nocow/> <features> <lazy_refcounts/> </features> @@ -424,6 +425,12 @@ 1.1 is used. If omitted, qemu-img default is used. Since 1.1.0 +
nocow
+
Turn off COW of the newly created volume. So far, this is only valid + for a file image in btrfs file system. It will improve performance when + the file image is used in VM. To create non-raw file images, it + requires QEMU version since 2.1. Since 1.2.7 +
features
Format-specific features. Only used for qcow2 now. Valid sub-elements are: diff --git a/docs/schemas/storagevol.rng b/docs/schemas/storagevol.rng index 3798476f03..1b2d4cccad 100644 --- a/docs/schemas/storagevol.rng +++ b/docs/schemas/storagevol.rng @@ -137,6 +137,11 @@ + + + + + diff --git a/src/conf/storage_conf.c b/src/conf/storage_conf.c index c79aebd0a4..69333f574a 100644 --- a/src/conf/storage_conf.c +++ b/src/conf/storage_conf.c @@ -1299,6 +1299,9 @@ virStorageVolDefParseXML(virStoragePoolDefPtr pool, virStringFreeList(version); } + if (virXPathNode("./target/nocow", ctxt)) + ret->target.nocow = true; + if (options->featureFromString && virXPathNode("./target/features", ctxt)) { if ((n = virXPathNodeSet("./target/features/*", ctxt, &nodes)) < 0) goto error; diff --git a/src/storage/storage_backend.c b/src/storage/storage_backend.c index fdcaadad77..dc835d36ba 100644 --- a/src/storage/storage_backend.c +++ b/src/storage/storage_backend.c @@ -37,6 +37,9 @@ #ifdef __linux__ # include # include +# ifndef FS_NOCOW_FL +# define FS_NOCOW_FL 0x00800000 /* Do not cow file */ +# endif #endif #if WITH_SELINUX @@ -453,6 +456,21 @@ virStorageBackendCreateRaw(virConnectPtr conn ATTRIBUTE_UNUSED, goto cleanup; } + if (vol->target.nocow) { +#ifdef __linux__ + int attr; + + /* Set NOCOW flag. This is an optimisation for btrfs. + * The FS_IOC_SETFLAGS ioctl return value will be ignored since any + * failure of this operation should not block the left work. + */ + if (ioctl(fd, FS_IOC_GETFLAGS, &attr) == 0) { + attr |= FS_NOCOW_FL; + ioctl(fd, FS_IOC_SETFLAGS, &attr); + } +#endif + } + if ((ret = createRawFile(fd, vol, inputvol)) < 0) /* createRawFile already reported the exact error. */ ret = -1; @@ -718,6 +736,7 @@ virStorageBackendCreateQemuImgOpts(char **opts, bool preallocate, int format, const char *compat, + bool nocow, virBitmapPtr features) { virBuffer buf = VIR_BUFFER_INITIALIZER; @@ -730,6 +749,8 @@ virStorageBackendCreateQemuImgOpts(char **opts, virBufferAddLit(&buf, "encryption=on,"); if (preallocate) virBufferAddLit(&buf, "preallocation=metadata,"); + if (nocow) + virBufferAddLit(&buf, "nocow=on,"); if (compat) virBufferAsprintf(&buf, "compat=%s,", compat); @@ -950,6 +971,7 @@ virStorageBackendCreateQemuImgCmd(virConnectPtr conn, do_encryption, preallocate, vol->target.format, compat, + vol->target.nocow, vol->target.features) < 0) { virCommandFree(cmd); return NULL; diff --git a/src/util/virstoragefile.h b/src/util/virstoragefile.h index 0ba746ab7d..c840aa06e2 100644 --- a/src/util/virstoragefile.h +++ b/src/util/virstoragefile.h @@ -247,6 +247,7 @@ struct _virStorageSource { * pool-specific enum for storage volumes */ virBitmapPtr features; char *compat; + bool nocow; virStoragePermsPtr perms; virStorageTimestampsPtr timestamps;