From: Chen Hanxiao <chenhanxiao(a)gmail.com&gt; Base upon patches from Roy Keene <rkeene(a)knightpoint.com&gt; Currently qemuDomainSaveMemory can save vm's config and memory to fd. It writes a magic QEMU_SAVE_PARTIAL firstly, then re-open it to change QEMU_SAVE_PARTIAL as QEMU_SAVE_MAGIC after a success write. For pipes this is not possible, attempting to re-open the pipe will not connect you to the same consumer. Seeking is also not possible on a pipe. This patch introduce VIR_DOMAIN_SAVE_PIPE. If set, write QEMU_SAVE_MAGIC directly. Try to write a regular file with VIR_DOMAIN_SAVE_PIPE is not supportted. This is useful to me for saving a VM state directly to Ceph RBD images without having an intermediate file. Cc: Roy Keene <rkeene(a)knightpoint.com&gt; Signed-off-by: Chen Hanxiao <chenhanxiao(a)gmail.com&gt; --- include/libvirt/libvirt-domain.h | 1 + src/qemu/qemu_driver.c | 71 ++++++++++++++++++++++++++++++---------- 2 files changed, 54 insertions(+), 18 deletions(-) diff --git a/include/libvirt/libvirt-domain.h b/include/libvirt/libvirt-domain.h index a8435ab..c3e4c15 100644 --- a/include/libvirt/libvirt-domain.h +++ b/include/libvirt/libvirt-domain.h @@ -1169,6 +1169,7 @@ typedef enum { VIR_DOMAIN_SAVE_BYPASS_CACHE = 1 << 0, /* Avoid file system cache pollution */ VIR_DOMAIN_SAVE_RUNNING = 1 << 1, /* Favor running over paused */ VIR_DOMAIN_SAVE_PAUSED = 1 << 2, /* Favor paused over running */ + VIR_DOMAIN_SAVE_PIPE = 1 << 3, /* Output is a pipe */ } virDomainSaveRestoreFlags; int virDomainSave (virDomainPtr domain, diff --git a/src/qemu/qemu_driver.c b/src/qemu/qemu_driver.c index 3517aa2..58422ac 100644 --- a/src/qemu/qemu_driver.c +++ b/src/qemu/qemu_driver.c @@ -3054,14 +3054,15 @@ qemuDomainSaveMemory(virQEMUDriverPtr driver, virQEMUSaveHeader header; bool bypassSecurityDriver = false; bool needUnlink = false; + bool canReopen = true; int ret = -1; int fd = -1; int directFlag = 0; virFileWrapperFdPtr wrapperFd = NULL; unsigned int wrapperFlags = VIR_FILE_WRAPPER_NON_BLOCKING; + struct stat statbuf; memset(&header, 0, sizeof(header)); - memcpy(header.magic, QEMU_SAVE_PARTIAL, sizeof(header.magic)); header.version = QEMU_SAVE_VERSION; header.was_running = was_running ? 1 : 0; header.compressed = compressed; @@ -3077,6 +3078,27 @@ qemuDomainSaveMemory(virQEMUDriverPtr driver, goto cleanup; } } + + /* + * Determine if this file is a PIPE, which could not be reopen. + */ + if (virFileExists(path)) { + fd = qemuOpenFile(driver, vm, path, O_RDONLY | O_NONBLOCK, NULL, NULL); + if (fd < 0) + goto cleanup; + if (fstat(fd, &statbuf) < 0) + goto cleanup; + if (S_ISFIFO(statbuf.st_mode)) { + if (flags & VIR_DOMAIN_SAVE_PIPE) { + canReopen = false; + } else { + virReportSystemError(EINVAL, _("%s is not PIPE"), path); + goto cleanup; + } + } + VIR_FORCE_CLOSE(fd); + } + fd = qemuOpenFile(driver, vm, path, O_WRONLY | O_TRUNC | O_CREAT | directFlag, &needUnlink, &bypassSecurityDriver); @@ -3089,6 +3111,16 @@ qemuDomainSaveMemory(virQEMUDriverPtr driver, if (!(wrapperFd = virFileWrapperFdNew(&fd, path, wrapperFlags))) goto cleanup; + /* Set the header magic. + * If the fd could be reopen, we'll update the magic after + * the saving completes successfully. + * Otherwise, include the final magic here, like pipe. + */ + if (canReopen) + memcpy(header.magic, QEMU_SAVE_PARTIAL, sizeof(header.magic)); + else + memcpy(header.magic, QEMU_SAVE_MAGIC, sizeof(header.magic)); + /* Write header to file, followed by XML */ if (qemuDomainSaveHeader(fd, path, domXML, &header) < 0) goto cleanup; @@ -3097,28 +3129,30 @@ qemuDomainSaveMemory(virQEMUDriverPtr driver, if (qemuMigrationToFile(driver, vm, fd, compressedpath, asyncJob) < 0) goto cleanup; - /* Touch up file header to mark image complete. */ + if (canReopen) { + /* Touch up file header to mark image complete. */ - /* Reopen the file to touch up the header, since we aren't set - * up to seek backwards on wrapperFd. The reopened fd will - * trigger a single page of file system cache pollution, but - * that's acceptable. */ - if (VIR_CLOSE(fd) < 0) { - virReportSystemError(errno, _("unable to close %s"), path); - goto cleanup; - } + /* Reopen the file to touch up the header, since we aren't set + * up to seek backwards on wrapperFd. The reopened fd will + * trigger a single page of file system cache pollution, but + * that's acceptable. */ + if (VIR_CLOSE(fd) < 0) { + virReportSystemError(errno, _("unable to close %s"), path); + goto cleanup; + } - if (virFileWrapperFdClose(wrapperFd) < 0) - goto cleanup; + if (virFileWrapperFdClose(wrapperFd) < 0) + goto cleanup; - if ((fd = qemuOpenFile(driver, vm, path, O_WRONLY, NULL, NULL)) < 0) - goto cleanup; + if ((fd = qemuOpenFile(driver, vm, path, O_WRONLY, NULL, NULL)) < 0) + goto cleanup; - memcpy(header.magic, QEMU_SAVE_MAGIC, sizeof(header.magic)); + memcpy(header.magic, QEMU_SAVE_MAGIC, sizeof(header.magic)); - if (safewrite(fd, &header, sizeof(header)) != sizeof(header)) { - virReportSystemError(errno, _("unable to write %s"), path); - goto cleanup; + if (safewrite(fd, &header, sizeof(header)) != sizeof(header)) { + virReportSystemError(errno, _("unable to write %s"), path); + goto cleanup; + } } if (VIR_CLOSE(fd) < 0) { @@ -3345,6 +3379,7 @@ qemuDomainSaveFlags(virDomainPtr dom, const char *path, const char *dxml, virCheckFlags(VIR_DOMAIN_SAVE_BYPASS_CACHE | VIR_DOMAIN_SAVE_RUNNING | + VIR_DOMAIN_SAVE_PIPE | VIR_DOMAIN_SAVE_PAUSED, -1); cfg = virQEMUDriverGetConfig(driver); -- 2.7.4

At 2016-12-08 20:08:11, "Peter Krempa" <pkrempa(a)redhat.com&gt; wrote: We need a flag to specify that we need to write QEMU_SAVE_MAGIC directly. Any suggestion for the name of this flag? [snip] My concern is that when we write to a pipe/fifo, if no one read it, we will hang. We should prevent from doing this only when we specify a flag. Regards, - Chen