Cleanup macros to set and retrieve blkptr birth times #15962
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It is compatible only until the upper bits are reused for something later. After that only systems having this code will be able to read the pool. Depending on the nature of these later changes I wonder if it could make sense to introduce feature flag here to avoid it or at least reduce transition effects later. Otherwise I am not sure what is the befit of freeing space now, if we'll need pretty strict feature flag for it later any way. We could just make the later feature(s) to cut the space from the birth time on as needed basis instead of reserving abstract 2x16bit now. |
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We can leave the upper 16-bits in place and just provide the macros so that we have a consistent way of manipulating the blkptr birth times. This would also be helpful to my future work. As you mentioned, once the new feature is ready, a determination of the feature flag would be necessary. I'm not sure if others features are looking at re-purposing the upper bits of the birth time and that's why I wanted to start this discussion. |
Sounds good to me. |
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grwilson
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I have updated the PR to only provide the macro changes. The changes to reduce the birth time fields in the blkptr pointer have been removed. |
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There exist a couple of macros that are used to update the blkptr birth times but they can often be confusing. For example, the BP_PHYSICAL_BIRTH() macro will provide either the physical birth time if it is set or else return back the logical birth time. The complement to this macro is BP_SET_BIRTH() which will set the logical birth time and set the physical birth time if they are not the same. Consumers may get confused when they are trying to get the physical birth time and use the BP_PHYSICAL_BIRTH() macro only to find out that the logical birth time is what is actually returned. This change cleans up these macros and makes them symmetrical. The same functionally is preserved but the name is changed. Instead of calling BP_PHYSICAL_BIRTH(), consumer can now call BP_GET_BIRTH(). In additional to cleaning up this naming conventions, two new sets of macros are introduced -- BP_[SET|GET]_LOGICAL_BIRTH() and BP_[SET|GET]_PHYSICAL_BIRTH. These new macros allow the consumer to get and set the specific birth time. As part of the cleanup, the unused GRID macros have been removed and that portion of the blkptr are currently unused. Signed-off-by: George Wilson <[email protected]>
There exist a couple of macros that are used to update the blkptr birth times but they can often be confusing. For example, the BP_PHYSICAL_BIRTH() macro will provide either the physical birth time if it is set or else return back the logical birth time. The complement to this macro is BP_SET_BIRTH() which will set the logical birth time and set the physical birth time if they are not the same. Consumers may get confused when they are trying to get the physical birth time and use the BP_PHYSICAL_BIRTH() macro only to find out that the logical birth time is what is actually returned. This change cleans up these macros and makes them symmetrical. The same functionally is preserved but the name is changed. Instead of calling BP_PHYSICAL_BIRTH(), consumer can now call BP_GET_BIRTH(). In additional to cleaning up this naming conventions, two new sets of macros are introduced -- BP_[SET|GET]_LOGICAL_BIRTH() and BP_[SET|GET]_PHYSICAL_BIRTH. These new macros allow the consumer to get and set the specific birth time. As part of the cleanup, the unused GRID macros have been removed and that portion of the blkptr are currently unused. Reviewed-by: Matthew Ahrens <[email protected]> Reviewed-by: Alexander Motin <[email protected]> Reviewed-by: Mark Maybee <[email protected]> Signed-off-by: George Wilson <[email protected]> Closes openzfs#15962
There exist a couple of macros that are used to update the blkptr birth times but they can often be confusing. For example, the BP_PHYSICAL_BIRTH() macro will provide either the physical birth time if it is set or else return back the logical birth time. The complement to this macro is BP_SET_BIRTH() which will set the logical birth time and set the physical birth time if they are not the same. Consumers may get confused when they are trying to get the physical birth time and use the BP_PHYSICAL_BIRTH() macro only to find out that the logical birth time is what is actually returned.
This PR cleans up these macros and makes them symmetrical. The same functionally is preserved but the name is changed. Consumers that used to call BP_PHYSICAL_BIRTH() will now call BP_GET_BIRTH(). In additional to cleaning up this naming conventions, two new sets of macros are introduced -- BP_[SET|GET]LOGICAL_BIRTH() and BP[SET|GET]_PHYSICAL_BIRTH. These new macros allow the consumer to get and set the specific birth time.