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SubjectRe: [PATCH 1/7] lib/vsprintf: add %*pg format specifier
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Joe Perches <joe@perches.com> writes:

> On Tue, 2015-03-31 at 20:01 +0400, Dmitry Monakhov wrote:
>> This allow to directly print block_device name.
>> Currently one should use bdevname() with temporal char buf[BDEVNAME_SIZE].
>> This is very ineffective because bloat stack usage for deep IO call-traces
> []
>> diff --git a/lib/vsprintf.c b/lib/vsprintf.c
> []
>> @@ -610,6 +613,23 @@ char *dentry_name(char *buf, char *end, const struct dentry *d, struct printf_sp
>> return buf;
>> }
>>
>> +#ifdef CONFIG_BLOCK
>> +static noinline_for_stack
>> +char *bdev_name(char *buf, char *end, struct block_device *bdev,
>> + struct printf_spec spec, const char *fmt)
>> +{
>> + struct gendisk *hd = bdev->bd_disk;
>
> Can you please use the same form as dentry_name and
> dereference the pointer in vsprintf not here as below.
Im not sure I've got your comments. Please elaborate.
As far as I can see vsprintf->pointer looks like follows:
dentry_name
case 'd':
return dentry_name(buf, end, ptr, spec, fmt);

No any special dereference logic here. Later dentry ptr dereferenced
and accessed inside dentry_name as usual. Same logic works for Ipv[46]
format specifiers.

***Copied comment from next email:
> Perhaps it would be useful to update the disk_name/bdevname
> functions to take a buffer length along with the char * so
> that buffer overflows could not occur.
disk_name() use snprintf which is bad candidate to use inside vsprintf.
>
> That would also allow this function to use bdevname directly.
I'll change bdevname() to use "%pg" format specifier in order to
eliminate code duplication.
>
>> @@ -1404,6 +1424,8 @@ int kptr_restrict __read_mostly;
>> * (default assumed to be phys_addr_t, passed by reference)
>> * - 'd[234]' For a dentry name (optionally 2-4 last components)
>> * - 'D[234]' Same as 'd' but for a struct file
>> + * - 'g' For block_device name (gendisk + partition number)
>> +
>> *
>> * Note: The difference between 'S' and 'F' is that on ia64 and ppc64
>> * function pointers are really function descriptors, which contain a
>> @@ -1552,6 +1574,11 @@ char *pointer(const char *fmt, char *buf, char *end, void *ptr,
>> return dentry_name(buf, end,
>> ((const struct file *)ptr)->f_path.dentry,
>> spec, fmt);
>> +#ifdef CONFIG_BLOCK
>> + case 'g':
>> + return bdev_name(buf, end, ptr, spec, fmt);
>> +#endif
>> +
>> }
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