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From "Pete Wyckoff (JIRA)" <j...@apache.org>
Subject [jira] Commented: (HADOOP-4108) FileSystem support for POSIX access method
Date Thu, 11 Sep 2008 19:05:45 GMT

    [ https://issues.apache.org/jira/browse/HADOOP-4108?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12630312#action_12630312

Pete Wyckoff commented on HADOOP-4108:

bq. To me FileSystem.access(path, mode) seems more intuitive.

I think it would be nice whenever possible to not invent new api/abstractions, so the POSIX
model is nice to keep.

Turning my performance note on its head,  when one wants to just get access, doing everything
else for constructing a FileStatus object is a waste. And also when doing a readdir on a directory
with 30,000 files, do I really need the access permissions of every file?

In practice because fuse (the first use case) has to support ls --color=auto, it has to cache
stat objects and support access being called for every file in a directory after doing a readdir,
so having the access result in the stat object is helpful.

> FileSystem support for POSIX access method
> ------------------------------------------
>                 Key: HADOOP-4108
>                 URL: https://issues.apache.org/jira/browse/HADOOP-4108
>             Project: Hadoop Core
>          Issue Type: New Feature
>          Components: fs
>            Reporter: Pete Wyckoff
>            Assignee: Pete Wyckoff
> From man access:
> {code}
>  int access(const char *pathname, int mode);
> {code}
>        access  checks  whether  the process would be allowed to read, write or test for
existence of the file (or other file system object) whose name is pathname.  If pathname is
a symbolic link permissions of the file referred to by this symbolic link are tested.
>        mode is a mask consisting of one or more of R_OK, W_OK, X_OK and F_OK.
>        R_OK, W_OK and X_OK request checking whether the file exists and has read, write
and execute permissions, respectively.  F_OK just requests checking for the existence of the
>        The tests depend on the permissions of the directories occurring in the path to
the file, as given in pathname, and on the permissions of directories and files referred to
by symbolic links encountered on the way.
>        The check is done with the processâs real uid and gid, rather than with the effective
ids as is done when actually attempting an operation.  This is to allow set-UID  programs
>        easily determine the invoking userâs authority.
>        Only  access  bits  are checked, not the file type or contents.  Therefore, if
a directory is found to be "writable," it probably means that files can be created in the
>        and not that the directory can be written as a file.  Similarly, a DOS file may
be found to be "executable," but the execve(2) call will still fail.
>        If the process has appropriate privileges, an implementation may indicate success
for X_OK even if none of the execute file permission bits are set.
>        On success (all requested permissions granted), zero is returned.  On error (at
least one bit in mode asked for a permission that is denied, or some other error occurred),
 -1  is
>        returned, and errno is set appropriately.

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