Re: [LTP] [PATCH 2/2] syscalls/rename/rename11.c: add ELOOP, EMLINK and EROFS error value tests

[chrubis@suse.cz]

Hi!
> Note: int rename(const char *old, const char *new);
> For EMLINK error value test: the file named by old is a directory and the
> link count of the parent directory of new would exceed {LINK_MAX}.
> 
> This test will work on ext2 and ext3 filesystem. But there is some difference in some
> linux distributions.
> 
> For example, in fedora19 and RHEL7.0Beta, the kernel configs for ext2/ext3/ext4 filesystems
> list below:
> # CONFIG_EXT2_FS is not set
> # CONFIG_EXT3_FS is not set
> CONFIG_EXT4_FS=m
> CONFIG_EXT4_USE_FOR_EXT23=y
> CONFIG_EXT4_FS_POSIX_ACL=y
> CONFIG_EXT4_FS_SECURITY=y
> 
> If kernel has the above config, ext2 or ext3 is disabled. Then when we mount ext2 or
> ext3 filesystem, the ext4 filesystem driver code will be used for ext2 or ext3 file
> system mounts. This allows users to reduce their compiled kernel size by using one
> file system driver for ext2, ext3, and ext4 file systems. That means though we mount
> a block device with ext2 filesystem in it, the kernel will possibely use ext4 driver
> code instead.
> 
> So for this EMLINK error value test, we have test in ext4 directly. But the max
> subdirectories(per directory) in ext4 is unlimited default(When the link count exceeds
> 65,000, it is reset to 1 and no longer increases.).

Is this expected behavior? Because if the ref counting resets to 1 the
fs will break when somebody tries to delete the file. Or is just the
number reported to userspace wrong?

> But EMLINK error value test need the directory have a valid LINK_MAX,
> so for ext4, we use mkfs to clear "dir_index" filesystem feature, then
> ext4 has a LINK_MAX:65000: mkfs.ext4 -O ^dir_index device

So this is the same problem as with XFS.

I still think that correct solution to this problem is to write a
function that detects if there is a limit on number of links given a
filesystem path. Then we can simply skip the EMLINK test if the number
of links is unlimited.

-- 
Cyril Hrubis
chrubis@suse.cz

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