For filesystems, ACLs are inherited according to the "aclinherit" property on the filesystem (or inherited from the project). Previous versions of software allowed four options for this setting: "discard", "noallow", "restricted", and "passthrough". The 2009.Q2.0.0 release introduces a new option, "passthrough-x", with slightly different semantics as described in the product documentation:
Same as "passthrough", except that the owner, group, and everyone ACL entries inherit the execute permission only if the file creation mode also requests the execute bit.
The "passthrough" mode is typically used to cause all "data" files to be created with an identical mode in a directory tree. An administrator sets up ACL inheritance so that all files are created with a mode, such as 0664 or 0666. This all works as expected for data files, but you might want to optionally include the execute bit from the file creation mode into the inherited ACL. One example is an output file that is generated from tools, such as "cc" or "gcc". If the inherited ACL does not include the execute bit, then the output executable from the compiler is not executable until you use chmod(1) to change the permissions for the file.
To use this mode, the storage pool must be upgraded. If you choose not to upgrade the pool and attempt to use this property, you will get an error indicating that the storage pool needs to be upgraded first. There is no other implication of applying this update, and it can be ignored if there is no need to use this new setting. Applying this update is equivalent to upgrading the on-disk ZFS pool to ZFS Pool Version Summary.
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