The qdiscs RED, GRED, SFQ and CHOKE use different subsets of the same pool of global RED flags. These are passed in tc_red_qopt.flags. However none of these qdiscs validate the flag field, and just copy it over wholesale to internal structures, and later dump it back. (An exception is GRED, which does validate for VQs -- however not for the main setup.) A broken userspace can therefore configure a qdisc with arbitrary unsupported flags, and later expect to see the flags on qdisc dump. The current ABI therefore allows storage of several bits of custom data to qdisc instances of the types mentioned above. How many bits, depends on which flags are meaningful for the qdisc in question. E.g. SFQ recognizes flags ECN and HARDDROP, and the rest is not interpreted. If SFQ ever needs to support ADAPTATIVE, it needs another way of doing it, and at the same time it needs to retain the possibility to store 6 bits of uninterpreted data. Likewise RED, which adds a new flag later in this patchset. To that end, this patch adds a new function, red_get_flags(), to split the passed flags of RED-like qdiscs to flags and user bits, and red_validate_flags() to validate the resulting configuration. It further adds a new attribute, TCA_RED_FLAGS, to pass arbitrary flags.
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| @@ -256,6 +256,7 @@ enum { · 255 unmodified lines | ||
| 256 | 256 | TCA_RED_PARMS, |
| 257 | 257 | TCA_RED_STAB, |
| 258 | 258 | TCA_RED_MAX_P, |
| 259 | + TCA_RED_FLAGS, /* bitfield32 */ | |
| 259 | 260 | __TCA_RED_MAX, |
| 260 | 261 | }; |
| 261 | 262 | |
| @@ -268,12 +269,27 @@ struct tc_red_qopt { · 6 unmodified lines | ||
| 268 | 269 | unsigned char Wlog; /* log(W) */ |
| 269 | 270 | unsigned char Plog; /* log(P_max/(qth_max-qth_min)) */ |
| 270 | 271 | unsigned char Scell_log; /* cell size for idle damping */ |
| 272 | + | |
| 273 | + /* This field can be used for flags that a RED-like qdisc has | |
| 274 | + * historically supported. E.g. when configuring RED, it can be used for | |
| 275 | + * ECN, HARDDROP and ADAPTATIVE. For SFQ it can be used for ECN, | |
| 276 | + * HARDDROP. Etc. Because this field has not been validated, and is | |
| 277 | + * copied back on dump, any bits besides those to which a given qdisc | |
| 278 | + * has assigned a historical meaning need to be considered for free use | |
| 279 | + * by userspace tools. | |
| 280 | + * | |
| 281 | + * Any further flags need to be passed differently, e.g. through an | |
| 282 | + * attribute (such as TCA_RED_FLAGS above). Such attribute should allow | |
| 283 | + * passing both recent and historic flags in one value. | |
| 284 | + */ | |
| 271 | 285 | unsigned char flags; |
| 272 | 286 | #define TC_RED_ECN 1 |
| 273 | 287 | #define TC_RED_HARDDROP 2 |
| 274 | 288 | #define TC_RED_ADAPTATIVE 4 |
| 275 | 289 | }; |
| 276 | 290 | |
| 291 | +#define TC_RED_HISTORIC_FLAGS (TC_RED_ECN | TC_RED_HARDDROP | TC_RED_ADAPTATIVE) | |
| 292 | + | |
| 277 | 293 | struct tc_red_xstats { |
| 278 | 294 | __u32 early; /* Early drops */ |
| 279 | 295 | __u32 pdrop; /* Drops due to queue limits */ |