Messages in this thread |  | | Date | Sun, 1 Sep 2002 16:10:01 +0200 | Subject | Re: [PATCH] Initial support for struct vfs_cred [0/1] | From | Trond Myklebust <> |
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>>>>> " " == Trond Myklebust <trond.myklebust@fys.uio.no> writes:
>>>>> " " == Luca Barbieri <ldb@ldb.ods.org> writes: >> For example, rather than this; > <snip>
>> you can just do this: >> - uid_t saved_fsuid = current->fsuid; >> + uid_t saved_fsuid = current->fscred.uid; >> kernel_cap_t saved_cap = current-> cap_effective; > But I don't want to have to do that at all. Why should I change
Just to follow up on why the above 'optimization' is just plain wrong.
You are forgetting that the fscred might simultaneously be referenced by an open struct file. Are you saying that this file should suddenly see its credential change? The alternative without copy on write is to make a full copy of the fscred every time we open a file or schedule some form of asynchronous I/O, and hence need to cache the current VFS credentials.
The copy-on-write rule is there in order to *minimize* the need to copy the cred. It works because changing the cred's entries is supposed to be a *rare* occurrence, whereas taking references and reading are common.
Cheers, Trond - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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