mv: skipping file...it was replaced

[Larry Reznick]

We have Mosix version 1.9.0 running on Red Hat 8.0 with the Linux 2.4.20 kernel. We now get an error from cp or mv complaining with the error message, "skipping file `[mfs-pathname]', as it was replaced while being copied". I've found and fixed the problem with a work-around, but there's a Mosix question you may want to look at.

The problem happens in fileutils-4.1.9-11, the current version. In sys2.h is a SAME_INODE() macro defined to compare both the st_ino and st_dev. If two statbufs passed to the macro compare the same for both components, the macro returns a TRUE. While that logic makes sense to me for comparing a source file with a destination file for cp or mv, there is one place in copy.c in the beginning of the function copy_reg() where the source file is compared with itself to see if a change has happened since the operation began. In copy_internal(), either stat() or lstat() is called on the source file to give the 1st statbuf. Later, copy_internal() calls copy_reg(), which immediately opens the source file then calls fstat() to give the 2nd statbuf.

Unfortunately, Mosix changes the st_dev when a file is opened on the /mfs filesystem. Therefore, what stat() & lstat() report is different from what fstat() reports, so cp & mv both think the source file has changed and abort the operation. I was able to correct the problem by using a different version of SAME_INODE() that compares only the st_ino at that stage, not st_dev. I can't think of any reason why a single file would change its device without changing its inode, so I think SAME_INODE() has been logically overused in copy.c.

I've added the following macro in sys2.h:

448a449,451
> #define SAME_INODE_ONLY(Stat_buf_1, Stat_buf_2) \
> ((Stat_buf_1).st_ino == (Stat_buf_2).st_ino)
>

Then, in copy.c, in the function copy_reg(), I've changed the first reference to SAME_INODE into SAME_INODE_ONLY:

239c239
< if (! SAME_INODE (*src_sb, src_open_sb))
---
> if (! SAME_INODE_ONLY (*src_sb, src_open_sb))

With these in place, cp & mv work correctly on the Mosix /mfs filesystem. I have also reported this to the Mosix and openMosix teams, suggesting that they may not want to change the st_dev that fstat() reports from what stat() and lstat() reports.

--Larry

--
Larry Reznick Sr Software Developer
Interact Devices, Inc 916-673-1860 x225
160 Blue Ravine Rd Suite B Fax 916-669-0035
Folsom, CA 95630-4718 idicorp.net




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