On Thu, Apr 26, 2012 at 5:23 AM, Luis R. Rodriguez <mcgrof@xxxxxxxxxxxxxxxx> wrote: > On Mon, Apr 23, 2012 at 9:47 PM, David Miller <davem@xxxxxxxxxxxxx> wrote: >> From: "Luis R. Rodriguez" <mcgrof@xxxxxxxxxxxxxxxx> >> Date: Mon, 23 Apr 2012 19:46:43 -0700 >> >>> From: "Luis R. Rodriguez" <mcgrof@xxxxxxxxxxxxxxxx> >>> >>> pr_fmt() is either defined or we redefine it. Typically >>> drivers define it prior to including printk.h but this >>> is done under the assumption that no other subsystem >>> it uses has already defined pr_fmt(). In such cases >>> pr_fmt() should be undefined and redefined. >>> >>> Doing this properly shaves down compilation time quite >>> considerably. >>> >>> Signed-off-by: Luis R. Rodriguez <mcgrof@xxxxxxxxxxxxxxxx> >> >> Every driver defines pr_fmt then includes the headers. I do not >> see any other place which performs the initial undef of pr_fmt >> like you want to start doing here. > > One example is, and that is where I got the hint: > > drivers/net/wireless/mwifiex/decl.h > >> If there is a reason we should start doing this, it would appear >> to be a universal reason, not one specific to this driver. > > Sure. > >> If that's the case, we should formally agree to this and then work >> on gradually converting all the drivers in reasonably sized chunks. > > Understood. > >> Either way I can't apply this patch as-is, sorry Luis. > > So the issue can occur if any parent header ends up defining this, > this could happen if a subsystem wants to define the pr_fmt in their > own header and a driver for example wants to override this. In theory > this does not occur but in practice this may vary and if we want to > ensure this does not happen perhaps the thing to do is to document > this as such. > > I just tested allmodconfig though and checked compilation for V=1 > against drivers/net/wireless/ and found no issues against linux-next > though so in practice at least for wireless networking it seems we are > squeaky clean in its usage. I'll test across the kernel though next to > see if there are any real violators of the assumption. Unfortunately > I've hit an issue with compiling allmodconfig already with linux-next > that is already reported so my homework will be to find a shiny > linux-next to compile test against allmodconfig. > > An area that this does clearly happen but that likely does not merit > and upstream change for is in the backport work compat that defines > this for older kernels and later we have to also backport users of > pr_fmt such as pr_emerg_once. Ultimately drivers will want to actually > then override this and in that case the undef is necessary as > otherwise you get the redefinition warning which incurs in practice a > considerable CPU performance hit at compilation time. Additionally Arend has pointed pointed out that previously printk.h was removed as a direct include as well given that kernel.h includes it already: https://lkml.org/lkml/2011/5/25/331 So this would be a second issue with this patch. Luis -- To unsubscribe from this list: send the line "unsubscribe linux-bluetooth" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
