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Document d_splice_alias() calling conventions for ->lookup() users.

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Short version: it does the right thing when given NULL or ERR_PTR(...)
and its calling conventions are chosen to have minimal PITA when
used in ->lookup() instances.

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
This commit is contained in:
Al Viro 2018-10-10 16:52:37 -04:00
parent 3837d208d8
commit 1a16dbaf79
1 changed files with 11 additions and 0 deletions
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11
Documentation/filesystems/porting
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@ -622,3 +622,14 @@ in your dentry operations instead.
alloc_file_clone(file, flags, ops) does not affect any caller's references.
On success you get a new struct file sharing the mount/dentry with the
original, on failure - ERR_PTR().
--
[recommended]
->lookup() instances doing an equivalent of
if (IS_ERR(inode))
return ERR_CAST(inode);
return d_splice_alias(inode, dentry);
don't need to bother with the check - d_splice_alias() will do the
right thing when given ERR_PTR(...) as inode. Moreover, passing NULL
inode to d_splice_alias() will also do the right thing (equivalent of
d_add(dentry, NULL); return NULL;), so that kind of special cases
also doesn't need a separate treatment.