xfsdump: Revert dump version bump for 32bit projid fix
PATCH 1/1 xfsdump: Revert dump version bump for 32bit projid fix
commit 1e309da7a4f7e2a2f456bf6b7cea4c5f1181cd36 fixed xfsdump to properly save & restore the top 16 bits of a 32-bit projid, which otherwise was being dropped (and restored as 0) in older xfsdump.
The original thought was to bump the dump version, so that we know whether the dump (may) have the top 16 bits filled in. In practice this would prevent older restores from restoring newer dumps, and losing the top 16 bits contained in these newer dumps.
However, in hindsight this appears to be of limited value. I propose that the dump version change is unuseful/unwanted for a couple reasons:
* There is no actual dump *format* change; the structure size is the same, and the top 16 bits were properly zeroed before; old restores will read these fixed dumps without problems and without restoring garbage. IOW, they will behave exactly as buggily as they did before. And worst case, if a dump containing the top 16 bits is mangled by an old restore, this can be easily remedied by simply re-restoring with updated userspace.
* We have no reliable method to know whether 32 bit project IDs are in use; the feature flag was not added to the GEOM call at the time of implementation. Therefore we cannot reliably bump to V4 only for projid32bit filesystems, and we cannot restrict V4 restores only to projid32bit filesystems. So the dump version is not useful for feature cross-checking purposes.
I spoke with wkendall via email, and although he may not have given it the most scrutiny (having moved on from xfsdump-land), he also felt that a version dump may not be warranted.
---
common/global.c +0 -1
@@ -281,7 +281,6 @@ global_version_check( u_int32_t version )case GLOBAL_HDR_VERSION_1 :case GLOBAL_HDR_VERSION_2 :case GLOBAL_HDR_VERSION_3 : -case GLOBAL_HDR_VERSION_4 :return BOOL_TRUE ;default :return BOOL_FALSE ;
common/global.h +2 -4
@@ -28,15 +28,13 @@#define GLOBAL_HDR_VERSION_1 1#define GLOBAL_HDR_VERSION_2 2#define GLOBAL_HDR_VERSION_3 3 -#define GLOBAL_HDR_VERSION_4 4 -/* version 4 adds 32-bit projid (projid_hi) -* version 3 uses the full 32-bit inode generation number in direnthdr_t. +/* version 3 uses the full 32-bit inode generation number in direnthdr_t. * version 2 adds encoding of holes and a change to on-tape inventory format. * version 1 adds extended file attribute dumping. * version 0 xfsrestore can't handle media produced * by version 1 xfsdump. */ -#define GLOBAL_HDR_VERSION GLOBAL_HDR_VERSION_4 +#define GLOBAL_HDR_VERSION GLOBAL_HDR_VERSION_3#define GLOBAL_HDR_STRING_SZ 0x100#define GLOBAL_HDR_TIME_SZ 4
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Quoted 21 lines · Eric Sandeen
commit
1e309da7a4f7e2a2f456bf6b7cea4c5f1181cd36fixed xfsdump to properly save & restore the top 16 bits of a 32-bit projid, which otherwise was being dropped (and restored as 0) in older xfsdump.The original thought was to bump the dump version, so that we know whether the dump (may) have the top 16 bits filled in. In practice this would prevent older restores from restoring newer dumps, and losing the top 16 bits contained in these newer dumps.
However, in hindsight this appears to be of limited value. I propose that the dump version change is unuseful/unwanted for a couple reasons:
* There is no actual dump *format* change; the structure size is the same, and the top 16 bits were properly zeroed before; old restores will read these fixed dumps without problems and without restoring garbage. IOW, they will behave exactly as buggily as they did before. And worst case, if a dump containing the top 16 bits is mangled by an old restore, this can be easily remedied by simply re-restoring with updated userspace.
Quoted 6 lines
* We have no reliable method to know whether 32 bit project IDs are in use; the feature flag was not added to the GEOM call at the time of implementation. Therefore we cannot reliably bump to V4 only for projid32bit filesystems, and we cannot restrict V4 restores only to projid32bit filesystems. So the dump version is not useful for feature cross-checking purposes.
Seems reasonable. Definitely solves most of the nasty problems you've been juggling caused by a version bump and 32bit projid detection. Do we have an xfstest that verifies these assumptions are valid?
Cheers,
Dave.
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Dave Chinner [email protected] _______________________________________________ xfs mailing list [email protected] http://oss.sgi.com/mailman/listinfo/xfs
Quoted 29 lines · Dave Chinner
Quoted 21 lines · Eric Sandeen
commit
1e309da7a4f7e2a2f456bf6b7cea4c5f1181cd36fixed xfsdump to properly save & restore the top 16 bits of a 32-bit projid, which otherwise was being dropped (and restored as 0) in older xfsdump.The original thought was to bump the dump version, so that we know whether the dump (may) have the top 16 bits filled in. In practice this would prevent older restores from restoring newer dumps, and losing the top 16 bits contained in these newer dumps.
However, in hindsight this appears to be of limited value. I propose that the dump version change is unuseful/unwanted for a couple reasons:
* There is no actual dump *format* change; the structure size is the same, and the top 16 bits were properly zeroed before; old restores will read these fixed dumps without problems and without restoring garbage. IOW, they will behave exactly as buggily as they did before. And worst case, if a dump containing the top 16 bits is mangled by an old restore, this can be easily remedied by simply re-restoring with updated userspace.
Quoted 6 lines
* We have no reliable method to know whether 32 bit project IDs are in use; the feature flag was not added to the GEOM call at the time of implementation. Therefore we cannot reliably bump to V4 only for projid32bit filesystems, and we cannot restrict V4 restores only to projid32bit filesystems. So the dump version is not useful for feature cross-checking purposes.
Quoted 4 lines
Seems reasonable. Definitely solves most of the nasty problems you've been juggling caused by a version bump and 32bit projid detection. Do we have an xfstest that verifies these assumptions are valid?
I'll whip up a test that tests what happens when restoring a dump w/ all 32 bits to a filesystem w/o the feature.
I'm not sure testing a restoration of an "old" dump to a 32-bit projid is too useful, it really just tests that the zeroed bits in the old dump image stay zeroed.
-Eric
Quoted 4 lines
Cheers,
Dave.
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Hey Eric,
Quoted 28 lines · Eric Sandeen
commit
1e309da7a4f7e2a2f456bf6b7cea4c5f1181cd36fixed xfsdump to properly save & restore the top 16 bits of a 32-bit projid, which otherwise was being dropped (and restored as 0) in older xfsdump.The original thought was to bump the dump version, so that we know whether the dump (may) have the top 16 bits filled in. In practice this would prevent older restores from restoring newer dumps, and losing the top 16 bits contained in these newer dumps.
However, in hindsight this appears to be of limited value. I propose that the dump version change is unuseful/unwanted for a couple reasons:
* There is no actual dump *format* change; the structure size is the same, and the top 16 bits were properly zeroed before; old restores will read these fixed dumps without problems and without restoring garbage. IOW, they will behave exactly as buggily as they did before. And worst case, if a dump containing the top 16 bits is mangled by an old restore, this can be easily remedied by simply re-restoring with updated userspace.
* We have no reliable method to know whether 32 bit project IDs are in use; the feature flag was not added to the GEOM call at the time of implementation. Therefore we cannot reliably bump to V4 only for projid32bit filesystems, and we cannot restrict V4 restores only to projid32bit filesystems. So the dump version is not useful for feature cross-checking purposes.
Quoted 3 lines
I spoke with wkendall via email, and although he may not have given it the most scrutiny (having moved on from xfsdump-land), he also felt that a version dump may not be warranted.
This looks fine to me. I still think that bumping the format version was probably the right thing to do. But in this case it's not so important that I'm inclined to push harder for it. It was good to understand some of the implications of doing that, so maybe next time we do need to bump the version we'll be ready.
Warning the user when he could be losing the top 16 bits of the project id is something for the would-be-nice list.
Regards,
Ben
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Hey Eric,
Quoted 28 lines · Eric Sandeen
commit
1e309da7a4f7e2a2f456bf6b7cea4c5f1181cd36fixed xfsdump to properly save & restore the top 16 bits of a 32-bit projid, which otherwise was being dropped (and restored as 0) in older xfsdump.The original thought was to bump the dump version, so that we know whether the dump (may) have the top 16 bits filled in. In practice this would prevent older restores from restoring newer dumps, and losing the top 16 bits contained in these newer dumps.
However, in hindsight this appears to be of limited value. I propose that the dump version change is unuseful/unwanted for a couple reasons:
* There is no actual dump *format* change; the structure size is the same, and the top 16 bits were properly zeroed before; old restores will read these fixed dumps without problems and without restoring garbage. IOW, they will behave exactly as buggily as they did before. And worst case, if a dump containing the top 16 bits is mangled by an old restore, this can be easily remedied by simply re-restoring with updated userspace.
* We have no reliable method to know whether 32 bit project IDs are in use; the feature flag was not added to the GEOM call at the time of implementation. Therefore we cannot reliably bump to V4 only for projid32bit filesystems, and we cannot restrict V4 restores only to projid32bit filesystems. So the dump version is not useful for feature cross-checking purposes.
Quoted 5 lines
I spoke with wkendall via email, and although he may not have given it the most scrutiny (having moved on from xfsdump-land), he also felt that a version dump may not be warranted.
Signed-off-by Eric Sandeen <[email protected]>
Pulled this into git://oss.sgi.com/xfs/cmds/xfsdump.git, master branch.
Regards,
Ben
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