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save: new public API to bypass file system cache on save/restore

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In order to choose whether to use O_DIRECT when saving a domain image
to a file, we need a new flag.  But virDomainSave was implemented
before our policy of all new APIs having a flag argument.  Likewise
for virDomainRestore when restoring from a file.

The new flag name is chosen as CACHE_BYPASS so as not to preclude
a future solution that uses posix_fadvise once the Linux kernel has
a smarter implementation of that interface.

* include/libvirt/libvirt.h.in (virDomainCreateFlags)
(virDomainCoreDumpFlags): Add a flag.
(virDomainSaveFlags, virDomainRestoreFlags): New prototypes.
* src/libvirt.c (virDomainSaveFlags, virDomainRestoreFlags): New API.
* src/libvirt_public.syms: Export them.
* src/driver.h (virDrvDomainSaveFlags, virDrvDomainRestoreFlags):
New driver callbacks.
This commit is contained in:
Eric Blake 2011-07-06 12:10:11 -06:00
parent 360e5ea144
commit ad0b912384
4 changed files with 219 additions and 6 deletions
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20
include/libvirt/libvirt.h.in
View File

@ -235,6 +235,7 @@ typedef enum {
VIR_DOMAIN_NONE = 0, /* Default behavior */
VIR_DOMAIN_START_PAUSED = 1 << 0, /* Launch guest in paused state */
VIR_DOMAIN_START_AUTODESTROY = 1 << 1, /* Automatically kill guest when virConnectPtr is closed */
VIR_DOMAIN_START_BYPASS_CACHE = 1 << 2, /* Avoid file system cache pollution */
} virDomainCreateFlags;
@ -659,6 +660,7 @@ typedef virDomainMemoryStatStruct *virDomainMemoryStatPtr;
typedef enum {
VIR_DUMP_CRASH = (1 << 0), /* crash after dump */
VIR_DUMP_LIVE = (1 << 1), /* live dump */
VIR_DUMP_BYPASS_CACHE = (1 << 2), /* avoid file system cache pollution */
} virDomainCoreDumpFlags;
/* Domain migration flags. */
@ -941,10 +943,28 @@ int virDomainResume (virDomainPtr domain);
/*
* Domain save/restore
*/
/**
* virDomainSaveRestoreFlags:
* Flags for use in virDomainSaveFlags(), virDomainManagedSave(), and
* virDomainRestoreFlags().
*/
typedef enum {
VIR_DOMAIN_SAVE_BYPASS_CACHE = 1 << 0, /* Avoid file system cache pollution */
} virDomainSaveRestoreFlags;
int virDomainSave (virDomainPtr domain,
const char *to);
int virDomainSaveFlags (virDomainPtr domain,
const char *to,
const char *dxml,
unsigned int flags);
int virDomainRestore (virConnectPtr conn,
const char *from);
int virDomainRestoreFlags (virConnectPtr conn,
const char *from,
const char *dxml,
unsigned int flags);
/*
* Managed domain save

12
src/driver.h
View File

@ -177,9 +177,19 @@ typedef int
typedef int
(*virDrvDomainSave) (virDomainPtr domain,
const char *to);
typedef int
(*virDrvDomainSaveFlags) (virDomainPtr domain,
const char *to,
const char *dxml,
unsigned int flags);
typedef int
(*virDrvDomainRestore) (virConnectPtr conn,
const char *from);
typedef int
(*virDrvDomainRestoreFlags) (virConnectPtr conn,
const char *from,
const char *dxml,
unsigned int flags);
typedef int
(*virDrvDomainCoreDump) (virDomainPtr domain,
const char *to,
@ -714,7 +724,9 @@ struct _virDriver {
virDrvDomainGetState domainGetState;
virDrvDomainGetControlInfo domainGetControlInfo;
virDrvDomainSave domainSave;
virDrvDomainSaveFlags domainSaveFlags;
virDrvDomainRestore domainRestore;
virDrvDomainRestoreFlags domainRestoreFlags;
virDrvDomainCoreDump domainCoreDump;
virDrvDomainScreenshot domainScreenshot;
virDrvDomainSetVcpus domainSetVcpus;

181
src/libvirt.c
View File

@ -2242,6 +2242,8 @@ error:
* listed as running anymore (this may be a problem).
* Use virDomainRestore() to restore a domain after saving.
*
* See virDomainSaveFlags() for more control.
*
* Returns 0 in case of success and -1 in case of failure.
*/
int
@ -2295,6 +2297,85 @@ error:
return -1;
}
/**
* virDomainSaveFlags:
* @domain: a domain object
* @to: path for the output file
* @dxml: (optional) XML config for adjusting guest xml used on restore
* @flags: bitwise-OR of virDomainSaveRestoreFlags
*
* This method will suspend a domain and save its memory contents to
* a file on disk. After the call, if successful, the domain is not
* listed as running anymore (this may be a problem).
* Use virDomainRestore() to restore a domain after saving.
*
* If the hypervisor supports it, @dxml can be used to alter
* host-specific portions of the domain XML that will be used when
* restoring an image. For example, it is possible to alter the
* backing filename that is associated with a disk device, in order to
* prepare for file renaming done as part of backing up the disk
* device while the domain is stopped.
*
* If @flags includes VIR_DOMAIN_SAVE_BYPASS_CACHE, then libvirt will
* attempt to bypass the file system cache while creating the file, or
* fail if it cannot do so for the given system; this can allow less
* pressure on file system cache, but also risks slowing saves to NFS.
*
* Returns 0 in case of success and -1 in case of failure.
*/
int
virDomainSaveFlags(virDomainPtr domain, const char *to,
const char *dxml, unsigned int flags)
{
virConnectPtr conn;
VIR_DOMAIN_DEBUG(domain, "to=%s dxml=%s flags=%x",
to, NULLSTR(dxml), flags);
virResetLastError();
if (!VIR_IS_CONNECTED_DOMAIN(domain)) {
virLibDomainError(VIR_ERR_INVALID_DOMAIN, __FUNCTION__);
virDispatchError(NULL);
return -1;
}
if (domain->conn->flags & VIR_CONNECT_RO) {
virLibDomainError(VIR_ERR_OPERATION_DENIED, __FUNCTION__);
goto error;
}
conn = domain->conn;
if (to == NULL) {
virLibDomainError(VIR_ERR_INVALID_ARG, __FUNCTION__);
goto error;
}
if (conn->driver->domainSaveFlags) {
int ret;
char *absolute_to;
/* We must absolutize the file path as the save is done out of process */
if (virFileAbsPath(to, &absolute_to) < 0) {
virLibConnError(VIR_ERR_INTERNAL_ERROR,
_("could not build absolute output file path"));
goto error;
}
ret = conn->driver->domainSaveFlags(domain, absolute_to, dxml, flags);
VIR_FREE(absolute_to);
if (ret < 0)
goto error;
return ret;
}
virLibConnError(VIR_ERR_NO_SUPPORT, __FUNCTION__);
error:
virDispatchError(domain->conn);
return -1;
}
/**
* virDomainRestore:
* @conn: pointer to the hypervisor connection
@ -2302,6 +2383,8 @@ error:
*
* This method will restore a domain saved to disk by virDomainSave().
*
* See virDomainRestoreFlags() for more control.
*
* Returns 0 in case of success and -1 in case of failure.
*/
int
@ -2352,6 +2435,80 @@ error:
return -1;
}
/**
* virDomainRestoreFlags:
* @conn: pointer to the hypervisor connection
* @from: path to the input file
* @dxml: (optional) XML config for adjusting guest xml used on restore
* @flags: bitwise-OR of virDomainSaveRestoreFlags
*
* This method will restore a domain saved to disk by virDomainSave().
*
* If the hypervisor supports it, @dxml can be used to alter
* host-specific portions of the domain XML that will be used when
* restoring an image. For example, it is possible to alter the
* backing filename that is associated with a disk device, in order to
* prepare for file renaming done as part of backing up the disk
* device while the domain is stopped.
*
* If @flags includes VIR_DOMAIN_SAVE_BYPASS_CACHE, then libvirt will
* attempt to bypass the file system cache while restoring the file, or
* fail if it cannot do so for the given system; this can allow less
* pressure on file system cache, but also risks slowing saves to NFS.
*
* Returns 0 in case of success and -1 in case of failure.
*/
int
virDomainRestoreFlags(virConnectPtr conn, const char *from, const char *dxml,
unsigned int flags)
{
VIR_DEBUG("conn=%p, from=%s, dxml=%s, flags=%x",
conn, from, NULLSTR(dxml), flags);
virResetLastError();
if (!VIR_IS_CONNECT(conn)) {
virLibConnError(VIR_ERR_INVALID_CONN, __FUNCTION__);
virDispatchError(NULL);
return -1;
}
if (conn->flags & VIR_CONNECT_RO) {
virLibConnError(VIR_ERR_OPERATION_DENIED, __FUNCTION__);
goto error;
}
if (from == NULL) {
virLibConnError(VIR_ERR_INVALID_ARG, __FUNCTION__);
goto error;
}
if (conn->driver->domainRestoreFlags) {
int ret;
char *absolute_from;
/* We must absolutize the file path as the restore is done out of process */
if (virFileAbsPath(from, &absolute_from) < 0) {
virLibConnError(VIR_ERR_INTERNAL_ERROR,
_("could not build absolute input file path"));
goto error;
}
ret = conn->driver->domainRestoreFlags(conn, absolute_from, dxml,
flags);
VIR_FREE(absolute_from);
if (ret < 0)
goto error;
return ret;
}
virLibConnError(VIR_ERR_NO_SUPPORT, __FUNCTION__);
error:
virDispatchError(conn);
return -1;
}
/**
* virDomainCoreDump:
* @domain: a domain object
@ -2362,6 +2519,17 @@ error:
* Note that for remote Xen Daemon the file path will be interpreted in
* the remote host.
*
* If @flags includes VIR_DUMP_CRASH, then leave the guest shut off with
* a crashed state after the dump completes. If @flags includes
* VIR_DUMP_LIVE, then make the core dump while continuing to allow
* the guest to run; otherwise, the guest is suspended during the dump.
* The above two flags are mutually exclusive.
*
* Additionally, if @flags includes VIR_DUMP_BYPASS_CACHE, then libvirt
* will attempt to bypass the file system cache while creating the file,
* or fail if it cannot do so for the given system; this can allow less
* pressure on file system cache, but also risks slowing saves to NFS.
*
* Returns 0 in case of success and -1 in case of failure.
*/
int
@ -6612,6 +6780,12 @@ error:
* libvirtd daemon. Any domains marked for auto destroy will
* block attempts at migration or save-to-file
*
* If the VIR_DOMAIN_START_BYPASS_CACHE flag is set, and there is a
* managed save file for this domain (created by virDomainManagedSave()),
* then libvirt will attempt to bypass the file system cache while restoring
* the file, or fail if it cannot do so for the given system; this can allow
* less pressure on file system cache, but also risks slowing loads from NFS.
*
* Returns 0 in case of success, -1 in case of error
*/
int
@ -14837,7 +15011,7 @@ error:
/**
* virDomainManagedSave:
* @dom: pointer to the domain
* @flags: optional flags currently unused
* @flags: bitwise-OR of virDomainSaveRestoreFlags
*
* This method will suspend a domain and save its memory contents to
* a file on disk. After the call, if successful, the domain is not
@ -14847,6 +15021,11 @@ error:
* restarted (automatically or via an explicit libvirt call).
* As a result any running domain is sure to not have a managed saved image.
*
* If @flags includes VIR_DOMAIN_SAVE_BYPASS_CACHE, then libvirt will
* attempt to bypass the file system cache while creating the file, or
* fail if it cannot do so for the given system; this can allow less
* pressure on file system cache, but also risks slowing saves to NFS.
*
* Returns 0 in case of success or -1 in case of failure
*/
int virDomainManagedSave(virDomainPtr dom, unsigned int flags)

2
src/libvirt_public.syms
View File

@ -468,6 +468,8 @@ LIBVIRT_0.9.3 {
LIBVIRT_0.9.4 {
global:
virDomainRestoreFlags;
virDomainSaveFlags;
virDomainUndefineFlags;
} LIBVIRT_0.9.3;