Re: [libvirt] [PATCH v4] libxl: implement virDomainBlockStats

On 07/22/2016 10:50 PM, Jim Fehlig wrote: > On 07/20/2016 04:48 PM, Joao Martins wrote: >> Introduce initial support for domainBlockStats API call that >> allow us to query block device statistics. openstack nova >> uses this API call to query block statistics, alongside >> virDomainMemoryStats and virDomainInterfaceStats. Note that >> this patch only introduces it for VBD for starters. QDisk >> would come in a separate patch series. >> >> A new statistics data structure is introduced to fit common >> statistics among others specific to the underlying block >> backends. For the VBD statistics on linux these are exported >> via sysfs on the path: >> >> "/sys/bus/xen-backend/devices/vbd-<domid>-<devid>/statistics" >> >> To calculate the block devno libxlDiskPathToID is introduced. > Too bad libxl or libxlutil doesn't provide such a function. Yeah :( Unfortunately the function is private to libxl. But we could get devno indirectly through libxl_device_disk_getinfo provided by libxl_diskinfo->devid field. But at the same time that function does much more than that i.e. 5 other xenstore reads being the reason why I didn't pursued this way initially. On the other hand while it's incurs more overhead for just calculating an ID, it's better towards unlikely adjustments on this area. I say unlikely because this hasn't changed for the past 6 years (Xen 4.0?), see xen commit e9703a9 ("libxl: Properly parse vbd name"). What do you think?

>> Each backend implements its own function to extract statistics >> and let there be handled the different platforms. >> >> VBD stats are exposed in reqs and number of sectors from >> blkback, and it's up to us to convert it to sector sizes. >> The sector size is gathered through xenstore in the device >> backend entry "physical-sector-size". >> >> BlockStatsFlags variant is also implemented which has the >> added benefit of getting the number of flush requests. >> >> Signed-off-by: Joao Martins <joao.m.martins(a)oracle.com&gt; >> --- >> Changes since v3: >> - No need for error in libxlDiskSectorSize() >> - Fix an identation issue. >> - Rework cleanup paths on libxlDiskSectorSize() >> - Do not unlock vm if libxlDomainObjEndJob() returns false and >> adjust to the newly introduced virDomainObjEndAPI() >> - Bump version to 2.1.0 >> >> Changes since v1: >> - Fix identation issues >> - Set ret to LIBXL_VBD_SECTOR_SIZE >> - Reuse VIR_STRDUP error instead of doing virReportError >> when we fail to set stats->backend >> - Change virAsprintf(...) error checking >> - Change error to VIR_ERR_OPERATION_FAILED when xenstore path >> does not exist and when failing to read stat. >> - Resolve issues with 'make syntax-check' with cppi installed. >> - Remove libxlDiskPathMatches in favor of using virutil >> virDiskNameParse to fetch disk and partition index. >> - Rename libxlDiskPathParse to libxlDiskPathToID and rework >> function to just convert disk and partition index to devno. >> - Bump version to 1.2.22 >> --- >> src/libxl/libxl_driver.c | 364 +++++++++++++++++++++++++++++++++++++++++++++++ >> 1 file changed, 364 insertions(+) >> >> diff --git a/src/libxl/libxl_driver.c b/src/libxl/libxl_driver.c >> index f153f69..189bfb5 100644 >> --- a/src/libxl/libxl_driver.c >> +++ b/src/libxl/libxl_driver.c >> @@ -30,6 +30,7 @@ >> #include <math.h> >> #include <libxl.h> >> #include <libxl_utils.h> >> +#include <xenstore.h> >> #include <fcntl.h> >> #include <regex.h> >> >> @@ -72,6 +73,7 @@ VIR_LOG_INIT("libxl.libxl_driver"); >> #define LIBXL_DOM_REQ_HALT 4 >> >> #define LIBXL_NB_TOTAL_CPU_STAT_PARAM 1 >> +#define LIBXL_NB_TOTAL_BLK_STAT_PARAM 6 >> >> #define HYPERVISOR_CAPABILITIES "/proc/xen/capabilities" >> #define HYPERVISOR_XENSTORED "/dev/xen/xenstored" >> @@ -100,6 +102,25 @@ struct _libxlOSEventHookInfo { >> int id; >> }; >> >> +/* Object used to store disk statistics across multiple xen backends */ >> +typedef struct _libxlBlockStats libxlBlockStats; >> +typedef libxlBlockStats *libxlBlockStatsPtr; >> +struct _libxlBlockStats { >> + long long rd_req; >> + long long rd_bytes; >> + long long wr_req; >> + long long wr_bytes; >> + long long f_req; >> + >> + char *backend; >> + union { >> + struct { >> + long long ds_req; >> + long long oo_req; >> + } vbd; >> + } u; >> +}; >> + >> /* Function declarations */ >> static int >> libxlDomainManagedSaveLoad(virDomainObjPtr vm, >> @@ -5031,6 +5052,347 @@ libxlDomainGetJobStats(virDomainPtr dom, >> } >> >> static int >> +libxlDiskPathToID(const char *virtpath) >> +{ >> + static char const* drive_prefix[] = {"xvd", "hd", "sd"}; >> + int disk, partition, chrused; >> + int fmt, id; >> + char *r; >> + size_t i; >> + >> + fmt = id = -1; >> + >> + /* Find any disk prefixes we know about */ >> + for (i = 0; i < ARRAY_CARDINALITY(drive_prefix); i++) { >> + if (STRPREFIX(virtpath, drive_prefix[i]) && >> + !virDiskNameParse(virtpath, &disk, &partition)) { >> + fmt = i; >> + break; >> + } >> + } >> + >> + /* Handle it same way as xvd */ >> + if (fmt < 0 && >> + (sscanf(virtpath, "d%ip%i%n", &disk, &partition, &chrused) >= 2 >> + && chrused == strlen(virtpath))) >> + fmt = 0; >> + >> + /* Test indexes ranges and calculate the device id */ >> + switch (fmt) { >> + case 0: /* xvd */ >> + if (disk <= 15 && partition <= 15) >> + id = (202 << 8) | (disk << 4) | partition; >> + else if ((disk <= ((1<<20)-1)) || partition <= 255) >> + id = (1 << 28) | (disk << 8) | partition; >> + break; >> + case 1: /* hd */ >> + if (disk <= 3 && partition <= 63) >> + id = ((disk < 2 ? 3 : 22) << 8) | ((disk & 1) << 6) | partition; >> + break; >> + case 2: /* sd */ >> + if (disk <= 15 && (partition <= 15)) >> + id = (8 << 8) | (disk << 4) | partition; >> + break; >> + default: >> + errno = virStrToLong_i(virtpath, &r, 0, &id); >> + if (errno || *r || id > INT_MAX) >> + id = -1; >> + break; > The purpose of the default case is not clear to me. Can you explain that a bit? > IIUC, virtpath would contain values such as xvda, sdc, or /path/to/image. virtpath would only contain device names (no image paths). This falltrough case is to have device number directly from unsigned long instead of parsing device name. See (xen) libxl commit 8ca0ed2cd ("libxl: fail to parse disk vpath if a disk+part number needed but unavailable") as docs/misc/vbd-interface.txt isn't exactly clear on this. Regardless probably doesn't make a lot of sense for libvirt since we can only have device names. I will probably just set "id = -1" or depending on your preference rely on libxl_device_disk_getinfo(..) returned devid.

>> + } >> + return id; >> +} >> + >> +#define LIBXL_VBD_SECTOR_SIZE 512 >> + >> +static int >> +libxlDiskSectorSize(int domid, int devno) >> +{ >> + char *path, *val; >> + struct xs_handle *handle; >> + int ret = LIBXL_VBD_SECTOR_SIZE; >> + unsigned int len; >> + >> + handle = xs_daemon_open_readonly(); >> + if (!handle) { >> + VIR_WARN("cannot read sector size"); >> + return ret; >> + } >> + >> + path = val = NULL; >> + if (virAsprintf(&path, "/local/domain/%d/device/vbd/%d/backend", >> + domid, devno) < 0) >> + goto cleanup; >> + >> + if ((val = xs_read(handle, XBT_NULL, path, &len)) == NULL) >> + goto cleanup; >> + >> + VIR_FREE(path); >> + if (virAsprintf(&path, "%s/physical-sector-size", val) < 0) >> + goto cleanup; >> + >> + VIR_FREE(val); >> + if ((val = xs_read(handle, XBT_NULL, path, &len)) == NULL) >> + goto cleanup; >> + >> + if (sscanf(val, "%d", &ret) != 1) >> + ret = LIBXL_VBD_SECTOR_SIZE; >> + >> + cleanup: >> + VIR_FREE(val); >> + VIR_FREE(path); >> + xs_daemon_close(handle); >> + return ret; >> +} >> + >> +static int >> +libxlDomainBlockStatsVBD(virDomainObjPtr vm, >> + const char *dev, >> + libxlBlockStatsPtr stats) > The stats parameter is unused when __linux__ is not defined. Otherwise, the > patch looks fine. Ah yes, and size will get declared but not used too. Would you prefer resorting to this syntax instead: #ifdef __linux__ static int libxlDomainBlockStatsVBD(virDomainObjPtr vm, const char *dev, libxlBlockStatsPtr stats) { ... } #else static int libxlDomainBlockStatsVBD(virDomainObjPtr vm, const char *dev ATTRIBUTE_UNUSED, libxlBlockStatsPtr stats ATTRIBUTE_UNUSED) { virReportError(VIR_ERR_OPERATION_UNSUPPORTED, "%s", _("platform unsupported")); return -1; } #endif Or in alternative moving __linux__ conditional above devno declaration and always set ATTRIBUTE_UNUSED on dev and stats params?