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Subject[PATCH 3/7] sysfs: Keep an nlink count on sysfs directories.
Date
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;
+ }
+}
+
+static void sysfs_dir_dec_nlink(struct sysfs_dirent *sd)
+{
+ /* Don't decrement if we overflowed an increment */
+ if (sd->s_nlink != 1)
+ sd->s_nlink--;
+}
+
/**
* __sysfs_add_one - add sysfs_dirent to parent without warning
* @acxt: addrm context to use
@@ -420,6 +438,7 @@ int __sysfs_add_one(struct sysfs_addrm_cxt *acxt, struct sysfs_dirent *sd)
return -EEXIST;

sd->s_parent = sysfs_get(acxt->parent_sd);
+ sysfs_dir_inc_nlink(sd->s_parent);

sysfs_link_sibling(sd);

@@ -512,6 +531,7 @@ void sysfs_remove_one(struct sysfs_addrm_cxt *acxt, struct sysfs_dirent *sd)

BUG_ON(sd->s_flags & SYSFS_FLAG_REMOVED);

+ sysfs_dir_dec_nlink(sd->s_parent);
sysfs_unlink_sibling(sd);

/* Update timestamps on the parent */
diff --git a/fs/sysfs/inode.c b/fs/sysfs/inode.c
index 104cbc1..f0172b3 100644
--- a/fs/sysfs/inode.c
+++ b/fs/sysfs/inode.c
@@ -201,18 +201,6 @@ static inline void set_inode_attr(struct inode * inode, struct iattr * iattr)
inode->i_ctime = iattr->ia_ctime;
}

-static int sysfs_count_nlink(struct sysfs_dirent *sd)
-{
- struct sysfs_dirent *child;
- int nr = 0;
-
- for (child = sd->s_dir.children; child; child = child->s_sibling)
- if (sysfs_type(child) == SYSFS_DIR)
- nr++;
-
- return nr + 2;
-}
-
static void sysfs_refresh_inode(struct sysfs_dirent *sd, struct inode *inode)
{
struct sysfs_inode_attrs *iattrs = sd->s_iattr;
@@ -228,8 +216,7 @@ static void sysfs_refresh_inode(struct sysfs_dirent *sd, struct inode *inode)
iattrs->ia_secdata_len);
}

- if (sysfs_type(sd) == SYSFS_DIR)
- inode->i_nlink = sysfs_count_nlink(sd);
+ inode->i_nlink = sd->s_nlink;
}

int sysfs_getattr(struct vfsmount *mnt, struct dentry *dentry, struct kstat *stat)
diff --git a/fs/sysfs/mount.c b/fs/sysfs/mount.c
index 4974995..372a32c 100644
--- a/fs/sysfs/mount.c
+++ b/fs/sysfs/mount.c
@@ -37,6 +37,7 @@ struct sysfs_dirent sysfs_root = {
.s_count = ATOMIC_INIT(1),
.s_flags = SYSFS_DIR,
.s_mode = S_IFDIR | S_IRWXU | S_IRUGO | S_IXUGO,
+ .s_nlink = 2,
.s_ino = 1,
};

diff --git a/fs/sysfs/sysfs.h b/fs/sysfs/sysfs.h
index 0417805..85d5c6c 100644
--- a/fs/sysfs/sysfs.h
+++ b/fs/sysfs/sysfs.h
@@ -67,6 +67,7 @@ struct sysfs_dirent {

unsigned int s_flags;
unsigned short s_mode;
+ unsigned short s_nlink;
ino_t s_ino;
struct sysfs_inode_attrs *s_iattr;
};
--
1.6.5.2.143.g8cc62


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