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exporting through symlinks/stat vs lstat in diod_walk() #17

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+1 −1 

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@pipcet @garlick
@pipcet
pipcet commented

Hi,
this (single-character) change fixes a problem for me when exporting through a symlink to a directory on a different file system. If "link" is such a symlink, lstat("link") and lstat("link/file") will have different device ids; that makes diod_walk call _statmnt("link/file"), which tries to stat("link/file/.."), which fails with ENOTDIR:

[pid 27405] lstat("/srv/nfs/git/initramfs-tools_0.120_amd64.changes", {st_mode=S_IFREG|0644, st_size=1713, ...}) = 0
[pid 27405] lstat("/srv/nfs/git", {st_mode=S_IFLNK|0777, st_size=13, ...}) = 0
[pid 27405] stat("/srv/nfs/git/initramfs-tools_0.120_amd64.changes", {st_mode=S_IFREG|0644, st_size=1713, ...}) = 0
[pid 27405] stat("/srv/nfs/git/initramfs-tools_0.120_amd64.changes/..", 0x7f13c4fe8a40) = -1 ENOTDIR (Not a directory)

I believe the correct thing to do is to stat(f->path), which follows the symlink and returns the same device as lstat(npath) if the latter is a file residing in f.

@pipcet pipcet use stat() rather than lstat() to decide whether a directory entry is a … 
mount point.

if /link is a link to a directory on a different file system,
lstat(/link) and lstat(/link/file) have different .st_devs, even though
/link/file is an ordinary file in a symlinked directory; stat(/link) and
lstat(/link/file) have the same .st_devs, so I believe we should be
testing that condition instead.
 299e16b
@garlick garlick merged commit 171ac34 into chaos:master
@pipcet pipcet deleted the pipcet:lstat-stat branch
@garlick garlick referenced this pull request
Open

create test for symlinked mount point #18

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Commits on Apr 18, 2015
  1. @pipcet

    use stat() rather than lstat() to decide whether a directory entry is a …

    pipcet authored 
    mount point.

if /link is a link to a directory on a different file system,
lstat(/link) and lstat(/link/file) have different .st_devs, even though
/link/file is an ordinary file in a symlinked directory; stat(/link) and
lstat(/link/file) have the same .st_devs, so I believe we should be
testing that condition instead.
    299e16b
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  1. +1 −1  diod/ops.c
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2  diod/ops.c
@@ -426,7 +426,7 @@ diod_walk (Npfid *fid, Npstr* wname, Npqid *wqid)
np_uerror (errno);
goto error_quiet;
}
- if (lstat (path_s (f->path), &sb2) < 0) {
+ if (stat (path_s (f->path), &sb2) < 0) {
np_uerror (errno);
goto error;
}
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