Re: [libvirt] [PATCH] util: Alter return value of virReadFCHost and fix mem leak

On Wed, Oct 12, 2016 at 09:20:29AM -0400, John Ferlan wrote: > > > On 10/12/2016 06:40 AM, Erik Skultety wrote: >> On Tue, Oct 11, 2016 at 05:25:49PM -0400, John Ferlan wrote: >>> https://bugzilla.redhat.com/show_bug.cgi?id=1357416 >>> >>> Rather than return a 0 or -1 and the *result string, return just the result >>> string to the caller. Alter all the callers to handle the different return. >>> >>> As a side effect or result of this, it's much clearer that we cannot just >>> assign the returned string into the scsi_host wwnn, wwpn, and fabric_wwn >>> fields - rather we should fetch a temporary string, then as long as our >>> fetch was good, VIR_FREE what may have been there, and STEAL what we just got. >>> This fixes a memory leak in the virNodeDeviceCreateXML code path through >>> find_new_device and nodeDeviceLookupSCSIHostByWWN which will continually >>> call nodeDeviceSysfsGetSCSIHostCaps until the expected wwnn/wwpn is found >>> in the device object capabilities. >>> >>> Signed-off-by: John Ferlan <jferlan(a)redhat.com&gt; >>> --- >>> >>> I suppose I could have made two patches out of this, but it felt like >>> overkill once I realized what the issue was. OK a third one line patch >>> could have been added to change the virGetFCHostNameByWWN comment as well, >>> but that'd really be overkill. >>> >>> src/node_device/node_device_linux_sysfs.c | 55 ++++++++++++------------------- >>> src/util/virutil.c | 34 ++++++++----------- >>> src/util/virutil.h | 9 +++-- >>> tests/fchosttest.c | 30 ++++++----------- >>> 4 files changed, 49 insertions(+), 79 deletions(-) >>> >>> diff --git a/src/node_device/node_device_linux_sysfs.c b/src/node_device/node_device_linux_sysfs.c >>> index 549d32c..be99c41 100644 >>> --- a/src/node_device/node_device_linux_sysfs.c >>> +++ b/src/node_device/node_device_linux_sysfs.c >>> @@ -44,8 +44,7 @@ VIR_LOG_INIT("node_device.node_device_linux_sysfs"); >>> int >>> nodeDeviceSysfsGetSCSIHostCaps(virNodeDevCapDataPtr d) >>> { >>> - char *max_vports = NULL; >>> - char *vports = NULL; >>> + char *tmp = NULL; >>> int ret = -1; >>> >>> if (virReadSCSIUniqueId(NULL, d->scsi_host.host, >>> @@ -59,64 +58,53 @@ nodeDeviceSysfsGetSCSIHostCaps(virNodeDevCapDataPtr d) >>> if (virIsCapableFCHost(NULL, d->scsi_host.host)) { >>> d->scsi_host.flags |= VIR_NODE_DEV_CAP_FLAG_HBA_FC_HOST; >>> >>> - if (virReadFCHost(NULL, >>> - d->scsi_host.host, >>> - "port_name", >>> - &d->scsi_host.wwpn) < 0) { >>> + if (!(tmp = virReadFCHost(NULL, d->scsi_host.host, "port_name"))) { >>> VIR_WARN("Failed to read WWPN for host%d", d->scsi_host.host); >>> goto cleanup; >>> } >>> + VIR_FREE(d->scsi_host.wwpn); >>> + VIR_STEAL_PTR(d->scsi_host.wwpn, tmp); >>> >>> - if (virReadFCHost(NULL, >>> - d->scsi_host.host, >>> - "node_name", >>> - &d->scsi_host.wwnn) < 0) { >>> + if (!(tmp = virReadFCHost(NULL, d->scsi_host.host, "node_name"))) { >>> VIR_WARN("Failed to read WWNN for host%d", d->scsi_host.host); >>> goto cleanup; >>> } >>> + VIR_FREE(d->scsi_host.wwnn); >>> + VIR_STEAL_PTR(d->scsi_host.wwnn, tmp); >>> >>> - if (virReadFCHost(NULL, >>> - d->scsi_host.host, >>> - "fabric_name", >>> - &d->scsi_host.fabric_wwn) < 0) { >>> + if (!(tmp = virReadFCHost(NULL, d->scsi_host.host, "fabric_name"))) { >>> VIR_WARN("Failed to read fabric WWN for host%d", >>> d->scsi_host.host); >>> goto cleanup; >>> } >>> + VIR_FREE(d->scsi_host.fabric_wwn); >>> + VIR_STEAL_PTR(d->scsi_host.fabric_wwn, tmp); >>> } >>> >> >> So if I understand correctly, the problem is basically that we did not call >> VIR_FREE on the data that had previously been filled to the virNodeDevCapData >> structure during replacing it with new data. So, we could just keep the >> signature of virReadFCHost as is and just add the VIR_FREE and VIR_STEAL_PTR >> to the function, thus there won't be any need to use VIR_FREE+STEAL repeatedly >> in here. >> > > True - we're overwriting the &d->scsi_host.{wwnn|wwpn|fabric_wwn} fields > and that's the primary issue (e.g. mem leak). > > While I understand your point, I'm not sure adding a VIR_FREE(*result) > to virReadFCHost just prior to the "if VIR_STRDUP(*result, p) < 0)" is a > proper solution since virReadFCHost does not "own" that memory. It > doesn't state that if *result has something in it, the code will perform > a VIR_FREE (although that's a nice convenience in this case). Sure it's > simple enough to add that comment, but then I believe that the I don't see a major problem here... > VIR_FREE() would have to be done at the top of the function; otherwise, > how does the caller distinguish which error occurred when -1 gets > returned and whether it should VIR_FREE itself? > Well, I have to admin that this^^ is a fair argument because there are 3 different spots where the function can fail, not that the caller could not check result for NULL but the fact that a function touched caller's argument and then failed would be just weird. So, yeah, good point. > Also, what if the caller didn't want the *result wiped out? What if it > was using it to compare what it found "this" time vs. what was present > in the data/file a previous time? That caller would then need to be > adjusted to pass a temporary variable anyway. Exactly, if a caller wanted to just compare 2 values - old and new one - they would use a temporary variable, that would IMHO be expected correct behaviour. Anyway, it's irrelevant now that I agree with your point above. > > I think for me most compelling reason to alter virReadFCHost is that it > follows the mindset of not returning two values from a function when one > is perfectly reasonable. >

> John > > BTW: The OCD would still kick in and want to change the comment below to > match the function name... Yeah, since the patch is going to be relatively beefy, this change will blend in fairly easily, so go ahead, ACK. Erik NOTE: I've recently switched to mutt and it's still quite new, so I forgot to hit 'g' for group reply, therefore most of this conversation 'officially' never happened, so CC'ng libvir-list at least for the last bit, I suppose the whole 'thread' is going to look odd, sigh.... > >>> -/* virGetHostNameByWWN: >>> +/* virGetFCHostNameByWWN: >> >> Normally, I'd say sure, you're absolutely right about not creating a separate >> patch for this kind of change, but once you make the adjustment I mentioned >> above none of the below changes will be necessary and thus this rename change >> would look sort of unrelated imho. >> >> ACK with the adjustment. >> >> Erik >> >>> * >>> * Iterate over the sysfs tree to get FC host name (e.g. host5) >>> * by the provided "wwnn,wwpn" pair. >>> @@ -2298,7 +2293,7 @@ virFindFCHostCapableVport(const char *sysfs_prefix) >>> if (!virIsCapableVport(prefix, host)) >>> continue; >>> >>> - if (virReadFCHost(prefix, host, "port_state", &state) < 0) { >>> + if (!(state = virReadFCHost(prefix, host, "port_state"))) { >>> VIR_DEBUG("Failed to read port_state for host%d", host); >>> continue; >>> } >>> @@ -2310,12 +2305,12 @@ virFindFCHostCapableVport(const char *sysfs_prefix) >>> } >>> VIR_FREE(state); >>> >>> - if (virReadFCHost(prefix, host, "max_npiv_vports", &max_vports) < 0) { >>> + if (!(max_vports = virReadFCHost(prefix, host, "max_npiv_vports"))) { >>> VIR_DEBUG("Failed to read max_npiv_vports for host%d", host); >>> continue; >>> } >>> >>> - if (virReadFCHost(prefix, host, "npiv_vports_inuse", &vports) < 0) { >>> + if (!(vports = virReadFCHost(prefix, host, "npiv_vports_inuse"))) { >>> VIR_DEBUG("Failed to read npiv_vports_inuse for host%d", host); >>> VIR_FREE(max_vports); >>> continue; >>> @@ -2379,14 +2374,13 @@ virGetSCSIHostNameByParentaddr(unsigned int domain ATTRIBUTE_UNUSED, >>> return NULL; >>> } >>> >>> -int >>> +char * >>> virReadFCHost(const char *sysfs_prefix ATTRIBUTE_UNUSED, >>> int host ATTRIBUTE_UNUSED, >>> - const char *entry ATTRIBUTE_UNUSED, >>> - char **result ATTRIBUTE_UNUSED) >>> + const char *entry ATTRIBUTE_UNUSED) >>> { >>> virReportSystemError(ENOSYS, "%s", _("Not supported on this platform")); >>> - return -1; >>> + return NULL; >>> } >>> >>> bool >>> diff --git a/src/util/virutil.h b/src/util/virutil.h >>> index 703ec53..8c0d83c 100644 >>> --- a/src/util/virutil.h >>> +++ b/src/util/virutil.h >>> @@ -182,11 +182,10 @@ virGetSCSIHostNameByParentaddr(unsigned int domain, >>> unsigned int slot, >>> unsigned int function, >>> unsigned int unique_id); >>> -int virReadFCHost(const char *sysfs_prefix, >>> - int host, >>> - const char *entry, >>> - char **result) >>> - ATTRIBUTE_NONNULL(3) ATTRIBUTE_NONNULL(4); >>> +char *virReadFCHost(const char *sysfs_prefix, >>> + int host, >>> + const char *entry) >>> + ATTRIBUTE_NONNULL(3); >>> >>> bool virIsCapableFCHost(const char *sysfs_prefix, int host); >>> bool virIsCapableVport(const char *sysfs_prefix, int host); >>> diff --git a/tests/fchosttest.c b/tests/fchosttest.c >>> index e9b89a7..a08a2e8 100644 >>> --- a/tests/fchosttest.c >>> +++ b/tests/fchosttest.c >>> @@ -68,35 +68,25 @@ test3(const void *data ATTRIBUTE_UNUSED) >>> char *vports = NULL; >>> int ret = -1; >>> >>> - if (virReadFCHost(TEST_FC_HOST_PREFIX, >>> - TEST_FC_HOST_NUM, >>> - "node_name", >>> - &wwnn) < 0) >>> + if (!(wwnn = virReadFCHost(TEST_FC_HOST_PREFIX, TEST_FC_HOST_NUM, >>> + "node_name"))) >>> return -1; >>> >>> - if (virReadFCHost(TEST_FC_HOST_PREFIX, >>> - TEST_FC_HOST_NUM, >>> - "port_name", >>> - &wwpn) < 0) >>> + if (!(wwpn = virReadFCHost(TEST_FC_HOST_PREFIX, TEST_FC_HOST_NUM, >>> + "port_name"))) >>> goto cleanup; >>> >>> - if (virReadFCHost(TEST_FC_HOST_PREFIX, >>> - TEST_FC_HOST_NUM, >>> - "fabric_name", >>> - &fabric_wwn) < 0) >>> + if (!(fabric_wwn = virReadFCHost(TEST_FC_HOST_PREFIX, TEST_FC_HOST_NUM, >>> + "fabric_name"))) >>> goto cleanup; >>> >>> - if (virReadFCHost(TEST_FC_HOST_PREFIX, >>> - TEST_FC_HOST_NUM, >>> - "max_npiv_vports", >>> - &max_vports) < 0) >>> + if (!(max_vports = virReadFCHost(TEST_FC_HOST_PREFIX, TEST_FC_HOST_NUM, >>> + "max_npiv_vports"))) >>> goto cleanup; >>> >>> >>> - if (virReadFCHost(TEST_FC_HOST_PREFIX, >>> - TEST_FC_HOST_NUM, >>> - "npiv_vports_inuse", >>> - &vports) < 0) >>> + if (!(vports = virReadFCHost(TEST_FC_HOST_PREFIX, TEST_FC_HOST_NUM, >>> + "npiv_vports_inuse"))) >>> goto cleanup; >>> >>> if (STRNEQ(expect_wwnn, wwnn) || >>> -- >>> 2.7.4 >>> >>> -- >>> libvir-list mailing list >>> libvir-list(a)redhat.com >>> https://www.redhat.com/mailman/listinfo/libvir-list