Re: [RFC][PATCH 1/6] prepare sysctls for containers

[Herbert Poetzl <herbert@13thfloor.at>]

On Mon, Mar 06, 2006 at 03:52:49PM -0800, Dave Hansen wrote:
> 
> Right now, sysctls can only deal with global variables.  This
> patch makes them a _little_ more flexible by allowing there to
> be an accessor function to get at the variable being changed,
> instead of it being global.
> 
> This allows the sysctls to be backed by variables that are,
> for instance, dynamically allocated and not available at
> compile-time.
> 
> This also provides a very simple mechanism to take things that
> are currently global and containerize them.

hmm, why do you call the sysctl_table_data() over and
over again? what's the purpose? what about sideeffects?

> Signed-off-by: Dave Hansen <haveblue@us.ibm.com>
> ---
> 
>  work-dave/include/linux/sysctl.h |    8 ++++
>  work-dave/kernel/sysctl.c        |   65 ++++++++++++++++++++++++++-------------
>  2 files changed, 52 insertions(+), 21 deletions(-)
> 
> diff -puN include/linux/sysctl.h~sysctls-for-containers include/linux/sysctl.h
> --- work/include/linux/sysctl.h~sysctls-for-containers	2006-03-06 15:41:55.000000000 -0800
> +++ work-dave/include/linux/sysctl.h	2006-03-06 15:41:55.000000000 -0800
> @@ -872,6 +872,7 @@ extern void sysctl_init(void);
>  
>  typedef struct ctl_table ctl_table;
>  
> +typedef void *ctl_data_access (void);
>  typedef int ctl_handler (ctl_table *table, int __user *name, int nlen,
>  			 void __user *oldval, size_t __user *oldlenp,
>  			 void __user *newval, size_t newlen, 
> @@ -957,6 +958,13 @@ struct ctl_table 
>  	int ctl_name;			/* Binary ID */
>  	const char *procname;		/* Text ID for /proc/sys, or zero */
>  	void *data;
> +	ctl_data_access *data_access;	/* set this to a function if you
> +					 * don't have a static place to point
> +					 * ->data at compile-time.  This
> +					 * function will be called to dynamically
> +					 * figure out a ->data pointer.  Do not
> +					 * set this and ->data at once.
> +					 */
>  	int maxlen;
>  	mode_t mode;
>  	ctl_table *child;
> diff -puN kernel/sysctl.c~sysctls-for-containers kernel/sysctl.c
> --- work/kernel/sysctl.c~sysctls-for-containers	2006-03-06 15:41:55.000000000 -0800
> +++ work-dave/kernel/sysctl.c	2006-03-06 15:41:55.000000000 -0800
> @@ -1197,6 +1197,24 @@ repeat:
>  	return -ENOTDIR;
>  }
>  

I'd expect that to be inline, and to vanish when
containers are disabled ...

> +void *sysctl_table_data(ctl_table *table)
> +{
> +	void *data;
> +
> +	if (table->data && table->data_access) {
> +		printk(KERN_WARNING
> +			"sysctl: data and accessor function set for: '%s'\n",
> +			table->procname);
> +		table->data = NULL;

why is ->data and ->data_access evil?

> +	}
> +
> +	data = table->data;
> +	if (!data && table->data_access)
> +		data = table->data_access();
> +
> +	return data;
> +}
> +
>  /* Perform the actual read/write of a sysctl table entry. */
>  int do_sysctl_strategy (ctl_table *table, 
>  			int __user *name, int nlen,
> @@ -1205,6 +1223,7 @@ int do_sysctl_strategy (ctl_table *table
>  {
>  	int op = 0, rc;
>  	size_t len;
> +	void *data;
>  
>  	if (oldval)
>  		op |= 004;
> @@ -1224,14 +1243,15 @@ int do_sysctl_strategy (ctl_table *table
>  
>  	/* If there is no strategy routine, or if the strategy returns
>  	 * zero, proceed with automatic r/w */
> -	if (table->data && table->maxlen) {
> +	data = sysctl_table_data(table);
> +	if (data && table->maxlen) {
>  		if (oldval && oldlenp) {
>  			if (get_user(len, oldlenp))
>  				return -EFAULT;
>  			if (len) {
>  				if (len > table->maxlen)
>  					len = table->maxlen;
> -				if(copy_to_user(oldval, table->data, len))
> +				if(copy_to_user(oldval, data, len))
>  					return -EFAULT;
>  				if(put_user(len, oldlenp))
>  					return -EFAULT;
> @@ -1241,7 +1261,7 @@ int do_sysctl_strategy (ctl_table *table
>  			len = newlen;
>  			if (len > table->maxlen)
>  				len = table->maxlen;
> -			if(copy_from_user(table->data, newval, len))
> +			if(copy_from_user(data, newval, len))
>  				return -EFAULT;
>  		}
>  	}
> @@ -1539,7 +1559,7 @@ int proc_dostring(ctl_table *table, int 
>  	char __user *p;
>  	char c;
>  	
> -	if (!table->data || !table->maxlen || !*lenp ||
> +	if (!sysctl_table_data(table) || !table->maxlen || !*lenp ||
>  	    (*ppos && !write)) {
>  		*lenp = 0;
>  		return 0;
> @@ -1557,18 +1577,18 @@ int proc_dostring(ctl_table *table, int 
>  		}
>  		if (len >= table->maxlen)
>  			len = table->maxlen-1;
> -		if(copy_from_user(table->data, buffer, len))
> +		if(copy_from_user(sysctl_table_data(table), buffer, len))
>  			return -EFAULT;
> -		((char *) table->data)[len] = 0;
> +		((char *) sysctl_table_data(table))[len] = 0;
>  		*ppos += *lenp;
>  	} else {
> -		len = strlen(table->data);
> +		len = strlen(sysctl_table_data(table));
>  		if (len > table->maxlen)
>  			len = table->maxlen;
>  		if (len > *lenp)
>  			len = *lenp;
>  		if (len)
> -			if(copy_to_user(buffer, table->data, len))
> +			if(copy_to_user(buffer, sysctl_table_data(table), len))
>  				return -EFAULT;
>  		if (len < *lenp) {
>  			if(put_user('\n', ((char __user *) buffer) + len))
> @@ -1636,13 +1656,13 @@ static int do_proc_dointvec(ctl_table *t
>  	char buf[TMPBUFLEN], *p;
>  	char __user *s = buffer;
>  	
> -	if (!table->data || !table->maxlen || !*lenp ||
> +	if (!sysctl_table_data(table) || !table->maxlen || !*lenp ||
>  	    (*ppos && !write)) {
>  		*lenp = 0;
>  		return 0;
>  	}
>  	
> -	i = (int *) table->data;
> +	i = (int *) sysctl_table_data(table);
>  	vleft = table->maxlen / sizeof(*i);
>  	left = *lenp;
>  
> @@ -1878,13 +1898,13 @@ static int do_proc_doulongvec_minmax(ctl
>  	char buf[TMPBUFLEN], *p;
>  	char __user *s = buffer;
>  	
> -	if (!table->data || !table->maxlen || !*lenp ||
> +	if (!sysctl_table_data(table) || !table->maxlen || !*lenp ||
>  	    (*ppos && !write)) {
>  		*lenp = 0;
>  		return 0;
>  	}
>  	
> -	i = (unsigned long *) table->data;
> +	i = (unsigned long *) sysctl_table_data(table);
>  	min = (unsigned long *) table->extra1;
>  	max = (unsigned long *) table->extra2;
>  	vleft = table->maxlen / sizeof(unsigned long);
> @@ -2230,7 +2250,9 @@ int sysctl_string(ctl_table *table, int 
>  		  void __user *oldval, size_t __user *oldlenp,
>  		  void __user *newval, size_t newlen, void **context)
>  {
> -	if (!table->data || !table->maxlen) 
> +	char *data = sysctl_table_data(table);
> +
> +	if (!data || !table->maxlen)
>  		return -ENOTDIR;
>  	
>  	if (oldval && oldlenp) {
> @@ -2238,7 +2260,7 @@ int sysctl_string(ctl_table *table, int 
>  		if (get_user(bufsize, oldlenp))
>  			return -EFAULT;
>  		if (bufsize) {
> -			size_t len = strlen(table->data), copied;
> +			size_t len = strlen(data), copied;
>  
>  			/* This shouldn't trigger for a well-formed sysctl */
>  			if (len > table->maxlen)
> @@ -2247,7 +2269,7 @@ int sysctl_string(ctl_table *table, int 
>  			/* Copy up to a max of bufsize-1 bytes of the string */
>  			copied = (len >= bufsize) ? bufsize - 1 : len;
>  
> -			if (copy_to_user(oldval, table->data, copied) ||
> +			if (copy_to_user(oldval, data, copied) ||
>  			    put_user(0, (char __user *)(oldval + copied)))
>  				return -EFAULT;
>  			if (put_user(len, oldlenp))
> @@ -2258,11 +2280,11 @@ int sysctl_string(ctl_table *table, int 
>  		size_t len = newlen;
>  		if (len > table->maxlen)
>  			len = table->maxlen;
> -		if(copy_from_user(table->data, newval, len))
> +		if(copy_from_user(data, newval, len))
>  			return -EFAULT;
>  		if (len == table->maxlen)
>  			len--;
> -		((char *) table->data)[len] = 0;
> +		data[len] = 0;
>  	}
>  	return 1;
>  }
> @@ -2320,7 +2342,7 @@ int sysctl_jiffies(ctl_table *table, int
>  			if (olen!=sizeof(int))
>  				return -EINVAL; 
>  		}
> -		if (put_user(*(int *)(table->data)/HZ, (int __user *)oldval) ||
> +		if (put_user(*(int *)(sysctl_table_data(table))/HZ, (int __user *)oldval) ||
>  		    (oldlenp && put_user(sizeof(int),oldlenp)))
>  			return -EFAULT;
>  	}
> @@ -2330,7 +2352,7 @@ int sysctl_jiffies(ctl_table *table, int
>  			return -EINVAL; 
>  		if (get_user(new, (int __user *)newval))
>  			return -EFAULT;
> -		*(int *)(table->data) = new*HZ; 
> +		*(int *)(sysctl_table_data(table)) = new*HZ;
>  	}
>  	return 1;
>  }
> @@ -2340,6 +2362,7 @@ int sysctl_ms_jiffies(ctl_table *table, 
>  		void __user *oldval, size_t __user *oldlenp,
>  		void __user *newval, size_t newlen, void **context)
>  {
> +	int *jiffies_ptr = sysctl_table_data(table);
>  	if (oldval) {
>  		size_t olen;
>  		if (oldlenp) { 
> @@ -2348,7 +2371,7 @@ int sysctl_ms_jiffies(ctl_table *table, 
>  			if (olen!=sizeof(int))
>  				return -EINVAL; 
>  		}
> -		if (put_user(jiffies_to_msecs(*(int *)(table->data)), (int __user *)oldval) ||
> +		if (put_user(jiffies_to_msecs(*jiffies_ptr), (int __user *)oldval) ||
>  		    (oldlenp && put_user(sizeof(int),oldlenp)))
>  			return -EFAULT;
>  	}
> @@ -2358,7 +2381,7 @@ int sysctl_ms_jiffies(ctl_table *table, 
>  			return -EINVAL; 
>  		if (get_user(new, (int __user *)newval))
>  			return -EFAULT;
> -		*(int *)(table->data) = msecs_to_jiffies(new);
> +		*jiffies_ptr = msecs_to_jiffies(new);
>  	}
>  	return 1;
>  }
> _

wouldn't some get/set helper make more sense?
i.e. some virtualizer and devirtualizer functions?

best,
Herbert

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