[lkml]   [2006]   [Aug]   [10]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
Messages in this thread
    SubjectRe: Urgent help needed on an NFS question, please help!!!
    I think nfs_compare_fh() might do the file handle verification task.
    However, it is still possible that AFTER C1 gets a valid file handle,
    BUT BEFORE C1 sends out the getattr() request, C2 deletes file X and
    creates a different file X1 which has the same inode number. Looks
    like the server side must verify the generation number carried in the
    file handle. Unfortunately, I didn't find this code at the server
    side. Any further insight on this?


    On 8/10/06, Neil Brown <> wrote:
    > On Thursday August 10, wrote:
    > > I just ran into a problem about NFS. It might be a fundmental problem
    > > of my current work. So please help!
    > >
    > > I am wondering how NFS guarantees a client didn't get wrong file
    > > attributes. Consider the following scenario:
    > >
    > > Suppose we have an NFS server S and two clients C1 and C2.
    > >
    > > Now C1 needs to access the file attributes of file X, it first does
    > > lookup() to get the file handle of file X.
    > >
    > > After C1 gets X's file handle and before C1 issues the getattr()
    > > request, C2 cuts in. Now C2 deletes file X and creates a new file X1,
    > > which has different name but the same inode number and device ID as
    > > the nonexistent file X.
    > >
    > > When C1 issues getattr() with the old file handle, it may get file
    > > attribute on wrong file X1. Is this true?
    > >
    > > If not, how NFS avoid this problem? Please direct me to the code that
    > > verifies this.
    > Generation numbers.
    > When the filesystem creates a new file it assigns a random number
    > as the 'generation' number and stores that in the inode.
    > This gets included in the filehandle, and checked when the filehandle
    > lookup is done.
    > Look for references to 'i_generation' in fs/ext3/*
    > Other files systems may approach this slightly differently, but the
    > filesystem is responsible for providing a unique-over-time filehandle,
    > and 'generation number' is the 'standard' way of doing this.
    > NeilBrown
    To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
    the body of a message to
    More majordomo info at
    Please read the FAQ at

     \ /
      Last update: 2006-08-10 08:07    [W:0.022 / U:7.364 seconds]
    ©2003-2017 Jasper Spaans. hosted at Digital OceanAdvertise on this site