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SubjectRe: [PATCH 3/7] sysfs: Keep an nlink count on sysfs directories.
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"Serge E. Hallyn" <serue@us.ibm.com> writes:

> Quoting Eric W. Biederman (ebiederm@xmission.com):
>> From: Eric W. Biederman <ebiederm@aristanetworks.com>
>>
>> On large directories sysfs_count_nlinks can be a significant
>> bottleneck, so keep a count in sysfs_dirent. If we exceed
>> the maximum number of directory entries we can store return
>> nlink of 1. An nlink of 1 matches what reiserfs does in
>> this case, and it let's find and similar utlities know that
>> we have a the directory nlink can not be used for optimization
>> purposes.
>>
>> Signed-off-by: Eric W. Biederman <ebiederm@aristanetworks.com>
>> ---
>> fs/sysfs/dir.c | 20 ++++++++++++++++++++
>> fs/sysfs/inode.c | 15 +--------------
>> fs/sysfs/mount.c | 1 +
>> fs/sysfs/sysfs.h | 1 +
>> 4 files changed, 23 insertions(+), 14 deletions(-)
>>
>> diff --git a/fs/sysfs/dir.c b/fs/sysfs/dir.c
>> index 5c4703d..1c364be 100644
>> --- a/fs/sysfs/dir.c
>> +++ b/fs/sysfs/dir.c
>> @@ -359,6 +359,7 @@ struct sysfs_dirent *sysfs_new_dirent(const char *name, umode_t mode, int type)
>> sd->s_name = name;
>> sd->s_mode = mode;
>> sd->s_flags = type;
>> + sd->s_nlink = type == SYSFS_DIR? 2:1;
>>
>> return sd;
>>
>> @@ -392,6 +393,23 @@ void sysfs_addrm_start(struct sysfs_addrm_cxt *acxt,
>> mutex_lock(&sysfs_mutex);
>> }
>>
>> +static void sysfs_dir_inc_nlink(struct sysfs_dirent *sd)
>> +{
>> + /* If we overflow force nlink to be 1 */
>> + if (sd->s_nlink > 1) {
>> + sd->s_nlink++;
>> + if (sd->s_nlink == 0)
>> + sd->s_nlink = 1;
>> + }
>> +}
>
> Now, the original code only ups nlink on parent if child is a dir.
> IIUC your code will now inc nlink for files as well. Is any userspace
> going to be confused by that?

Good point. nlink should only be upped for directories.

Eric


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