提交 519a1c43 编写于 作者: E Eric Blake

save: add virFileDirectFd wrapper type

O_DIRECT has stringent requirements.  Rather than make lots of changes
at each site that wants to use O_DIRECT, it is easier to offload
the work through a helper process that mirrors the I/O between a
pipe and the actual direct fd, so that the other end of the pipe
no longer has to worry about constraints.

Plus, if the kernel ever gains better posix_fadvise support, then we
only have to touch a single file to let all callers benefit from a
more efficient way to avoid file system caching.

* src/util/virfile.h (virFileDirectFdFlag, virFileDirectFdNew)
(virFileDirectFdClose, virFileDirectFdFree): New prototypes.
* src/util/virdirect.c: Implement new wrapper object.
* src/libvirt_private.syms (virfile.h): Export new symbols.
* cfg.mk (useless_free_options): Add to list.
* po/POTFILES.in: Add new translations.
上级 12291656
...@@ -120,6 +120,7 @@ useless_free_options = \ ...@@ -120,6 +120,7 @@ useless_free_options = \
--name=virDomainSoundDefFree \ --name=virDomainSoundDefFree \
--name=virDomainVideoDefFree \ --name=virDomainVideoDefFree \
--name=virDomainWatchdogDefFree \ --name=virDomainWatchdogDefFree \
--name=virFileDirectFdFree \
--name=virHashFree \ --name=virHashFree \
--name=virInterfaceDefFree \ --name=virInterfaceDefFree \
--name=virInterfaceIpDefFree \ --name=virInterfaceIpDefFree \
......
...@@ -122,6 +122,7 @@ src/util/storage_file.c ...@@ -122,6 +122,7 @@ src/util/storage_file.c
src/util/sysinfo.c src/util/sysinfo.c
src/util/util.c src/util/util.c
src/util/viraudit.c src/util/viraudit.c
src/util/virfile.c
src/util/virterror.c src/util/virterror.c
src/util/xml.c src/util/xml.c
src/vbox/vbox_MSCOMGlue.c src/vbox/vbox_MSCOMGlue.c
......
...@@ -1096,6 +1096,10 @@ virAuditSend; ...@@ -1096,6 +1096,10 @@ virAuditSend;
# virfile.h # virfile.h
virFileClose; virFileClose;
virFileDirectFdClose;
virFileDirectFdFlag;
virFileDirectFdFree;
virFileDirectFdNew;
virFileFclose; virFileFclose;
virFileFdopen; virFileFdopen;
......
...@@ -23,10 +23,24 @@ ...@@ -23,10 +23,24 @@
*/ */
#include <config.h> #include <config.h>
#include "internal.h"
#include "virfile.h"
#include <fcntl.h>
#include <sys/stat.h>
#include <unistd.h> #include <unistd.h>
#include "virfile.h" #include "command.h"
#include "configmake.h"
#include "memory.h"
#include "virterror_internal.h"
#define VIR_FROM_THIS VIR_FROM_NONE
#define virFileError(code, ...) \
virReportErrorHelper(VIR_FROM_THIS, code, __FILE__, \
__FUNCTION__, __LINE__, __VA_ARGS__)
int virFileClose(int *fdptr, bool preserve_errno) int virFileClose(int *fdptr, bool preserve_errno)
{ {
...@@ -78,3 +92,162 @@ FILE *virFileFdopen(int *fdptr, const char *mode) ...@@ -78,3 +92,162 @@ FILE *virFileFdopen(int *fdptr, const char *mode)
return file; return file;
} }
/* Opaque type for managing a wrapper around an O_DIRECT fd. For now,
* read-write is not supported, just a single direction. */
struct _virFileDirectFd {
virCommandPtr cmd; /* Child iohelper process to do the I/O. */
};
/**
* virFileDirectFdFlag:
*
* Returns 0 if the kernel can avoid file system cache pollution
* without any additional flags, O_DIRECT if the original fd must be
* opened in direct mode, or -1 if there is no support for bypassing
* the file system cache.
*/
int
virFileDirectFdFlag(void)
{
/* XXX For now, Linux posix_fadvise is not powerful enough to
* avoid O_DIRECT. */
return O_DIRECT ? O_DIRECT : -1;
}
/**
* virFileDirectFdNew:
* @fd: pointer to fd to wrap
* @name: name of fd, for diagnostics
*
* Update *FD (created with virFileDirectFdFlag() among the flags to
* open()) to ensure that all I/O to that file will bypass the system
* cache. This must be called after open() and optional fchown() or
* fchmod(), but before any seek or I/O, and only on seekable fd. The
* file must be O_RDONLY (to read the entire existing file) or
* O_WRONLY (to write to an empty file). In some cases, *FD is
* changed to a non-seekable pipe; in this case, the caller must not
* do anything further with the original fd.
*
* On success, the new wrapper object is returned, which must be later
* freed with virFileDirectFdFree(). On failure, *FD is unchanged, an
* error message is output, and NULL is returned.
*/
virFileDirectFdPtr
virFileDirectFdNew(int *fd, const char *name)
{
virFileDirectFdPtr ret = NULL;
bool output = false;
int pipefd[2] = { -1, -1 };
int mode = -1;
/* XXX support posix_fadvise rather than spawning a child, if the
* kernel support for that is decent enough. */
if (!O_DIRECT) {
virFileError(VIR_ERR_INTERNAL_ERROR, "%s",
_("O_DIRECT unsupported on this platform"));
return NULL;
}
if (VIR_ALLOC(ret) < 0) {
virReportOOMError();
return NULL;
}
#ifdef F_GETFL
/* Mingw lacks F_GETFL, but it also lacks O_DIRECT so didn't get
* here in the first place. All other platforms reach this
* line. */
mode = fcntl(*fd, F_GETFL);
#endif
if (mode < 0) {
virFileError(VIR_ERR_INTERNAL_ERROR, _("invalid fd %d for %s"),
*fd, name);
goto error;
} else if ((mode & O_ACCMODE) == O_WRONLY) {
output = true;
} else if ((mode & O_ACCMODE) != O_RDONLY) {
virFileError(VIR_ERR_INTERNAL_ERROR, _("unexpected mode %x for %s"),
mode & O_ACCMODE, name);
goto error;
}
if (pipe2(pipefd, O_CLOEXEC) < 0) {
virFileError(VIR_ERR_INTERNAL_ERROR,
_("unable to create pipe for %s"), name);
goto error;
}
ret->cmd = virCommandNewArgList(LIBEXECDIR "/libvirt_iohelper",
name, "0", NULL);
if (output) {
virCommandSetInputFD(ret->cmd, pipefd[0]);
virCommandSetOutputFD(ret->cmd, fd);
virCommandAddArg(ret->cmd, "1");
} else {
virCommandSetInputFD(ret->cmd, *fd);
virCommandSetOutputFD(ret->cmd, &pipefd[1]);
virCommandAddArg(ret->cmd, "0");
}
if (virCommandRunAsync(ret->cmd, NULL) < 0)
goto error;
if (VIR_CLOSE(pipefd[!output]) < 0) {
virFileError(VIR_ERR_INTERNAL_ERROR, "%s", _("unable to close pipe"));
goto error;
}
VIR_FORCE_CLOSE(*fd);
*fd = pipefd[output];
return ret;
error:
VIR_FORCE_CLOSE(pipefd[0]);
VIR_FORCE_CLOSE(pipefd[1]);
virFileDirectFdFree(ret);
return NULL;
}
/**
* virFileDirectFdClose:
* @dfd: direct fd wrapper, or NULL
*
* If DFD is valid, then ensure that I/O has completed, which may
* include reaping a child process. Return 0 if all data for the
* wrapped fd is complete, or -1 on failure with an error emitted.
* This function intentionally returns 0 when DFD is NULL, so that
* callers can conditionally create a virFileDirectFd wrapper but
* unconditionally call the cleanup code. To avoid deadlock, only
* call this after closing the fd resulting from virFileDirectFdNew().
*/
int
virFileDirectFdClose(virFileDirectFdPtr dfd)
{
if (!dfd)
return 0;
return virCommandWait(dfd->cmd, NULL);
}
/**
* virFileDirectFdFree:
* @dfd: direct fd wrapper, or NULL
*
* Free all remaining resources associated with DFD. If
* virFileDirectFdClose() was not previously called, then this may
* discard some previous I/O. To avoid deadlock, only call this after
* closing the fd resulting from virFileDirectFdNew().
*/
void
virFileDirectFdFree(virFileDirectFdPtr dfd)
{
if (!dfd)
return;
virCommandFree(dfd->cmd);
VIR_FREE(dfd);
}
...@@ -50,4 +50,19 @@ FILE *virFileFdopen(int *fdptr, const char *mode) ATTRIBUTE_RETURN_CHECK; ...@@ -50,4 +50,19 @@ FILE *virFileFdopen(int *fdptr, const char *mode) ATTRIBUTE_RETURN_CHECK;
# define VIR_FORCE_CLOSE(FD) ignore_value(virFileClose(&(FD), true)) # define VIR_FORCE_CLOSE(FD) ignore_value(virFileClose(&(FD), true))
# define VIR_FORCE_FCLOSE(FILE) ignore_value(virFileFclose(&(FILE), true)) # define VIR_FORCE_FCLOSE(FILE) ignore_value(virFileFclose(&(FILE), true))
/* Opaque type for managing a wrapper around an O_DIRECT fd. */
struct _virFileDirectFd;
typedef struct _virFileDirectFd virFileDirectFd;
typedef virFileDirectFd *virFileDirectFdPtr;
int virFileDirectFdFlag(void);
virFileDirectFdPtr virFileDirectFdNew(int *fd, const char *name)
ATTRIBUTE_NONNULL(1) ATTRIBUTE_NONNULL(2) ATTRIBUTE_RETURN_CHECK;
int virFileDirectFdClose(virFileDirectFdPtr dfd);
void virFileDirectFdFree(virFileDirectFdPtr dfd);
#endif /* __VIR_FILES_H */ #endif /* __VIR_FILES_H */
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