Messages in this thread Patch in this message | | | From | Andries.Brouwer@cwi ... | Date | Thu, 22 May 2003 21:09:43 +0200 (MEST) | Subject | [patch?] truncate and timestamps |
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Investigating why some SuSE init script no longer works, I find: The shell command > file does not update the time stamp of file in case it existed and had size 0. The corresponding system call is open(file, O_WRONLY | O_TRUNC);
Time stamp here is st_mtime, and the behaviour is not unreasonable: after all, the contents do not change.
And indeed, in do_truncate() we have newattrs.ia_valid = ATTR_SIZE | ATTR_CTIME; that is, ATTR_MTIME is not mentioned.
Older Linux systems did update st_mtime, old FreeBSD systems did not, SunOS 5.7 does, SunOS 5.8 does not. There is no uniform Unix behaviour.
Remains the question what POSIX says. For opening with O_TRUNC, and for the ftruncate system call POSIX has always said and still says: st_ctime and st_mtime are updated. For the truncate call POSIX.1-2001 says: st_ctime and st_mtime are updated if the size changed.
If we want to follow this, then do_truncate() needs an additional parameter indicating what kind of call we have. A little bit ugly. A possible patch follows.
Andries
------------------ diff -u --recursive --new-file -X /linux/dontdiff a/fs/exec.c b/fs/exec.c --- a/fs/exec.c Thu May 22 13:17:02 2003 +++ b/fs/exec.c Thu May 22 20:14:02 2003 @@ -1352,7 +1352,7 @@ goto close_fail; if (!file->f_op->write) goto close_fail; - if (do_truncate(file->f_dentry, 0) != 0) + if (do_truncate(file->f_dentry, 0, 1) != 0) goto close_fail; retval = binfmt->core_dump(signr, regs, file); diff -u --recursive --new-file -X /linux/dontdiff a/fs/namei.c b/fs/namei.c --- a/fs/namei.c Thu May 22 13:17:02 2003 +++ b/fs/namei.c Thu May 22 20:13:41 2003 @@ -1178,7 +1178,7 @@ if (!error) { DQUOT_INIT(inode); - error = do_truncate(dentry, 0); + error = do_truncate(dentry, 0, 1); } put_write_access(inode); if (error) diff -u --recursive --new-file -X /linux/dontdiff a/fs/open.c b/fs/open.c --- a/fs/open.c Thu May 22 13:17:02 2003 +++ b/fs/open.c Thu May 22 20:15:25 2003 @@ -75,7 +75,7 @@ return error; } -int do_truncate(struct dentry *dentry, loff_t length) +int do_truncate(struct dentry *dentry, loff_t length, int update_timestamp) { int err; struct iattr newattrs; @@ -85,7 +85,9 @@ return -EINVAL; newattrs.ia_size = length; - newattrs.ia_valid = ATTR_SIZE | ATTR_CTIME; + newattrs.ia_valid = ATTR_SIZE; + if (update_timestamp || length != dentry->d_inode->i_size) + newattrs.ia_valid |= ATTR_CTIME | ATTR_MTIME; down(&dentry->d_inode->i_sem); err = notify_change(dentry, &newattrs); up(&dentry->d_inode->i_sem); @@ -142,7 +144,7 @@ error = locks_verify_truncate(inode, NULL, length); if (!error) { DQUOT_INIT(inode); - error = do_truncate(nd.dentry, length); + error = do_truncate(nd.dentry, length, 0); } put_write_access(inode); @@ -194,7 +196,7 @@ error = locks_verify_truncate(inode, file, length); if (!error) - error = do_truncate(dentry, length); + error = do_truncate(dentry, length, 1); out_putf: fput(file); out: diff -u --recursive --new-file -X /linux/dontdiff a/include/linux/fs.h b/include/linux/fs.h --- a/include/linux/fs.h Thu May 22 13:17:05 2003 +++ b/include/linux/fs.h Thu May 22 20:14:39 2003 @@ -1019,7 +1019,7 @@ asmlinkage long sys_open(const char __user *, int, int); asmlinkage long sys_close(unsigned int); /* yes, it's really unsigned */ -extern int do_truncate(struct dentry *, loff_t start); +extern int do_truncate(struct dentry *, loff_t start, int update_timestamp); extern struct file *filp_open(const char *, int, int); extern struct file * dentry_open(struct dentry *, struct vfsmount *, int); - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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