When printing legacy sysctls print the warning message for each of them only once. This way there is a guarantee the syslog won't be flooded for any sane program. The original attempt at this made the tables non const and stored the flag inline. Linus suggested using a separate hash table for this, this is based on a code snippet from him. The hash implies this is not exact and can sometimes not print a new sysctl due to a hash collision, but in practice this should not be a problem I used a FNV32 hash over the binary string with a 32byte bitmap. This gives relatively little collisions when all the predefined binary sysctls are hashed: size 256 bucket length number 0: [25] 1: [67] 2: [88] 3: [47] 4: [22] 5: [6] 6: [1] The worst case is a single collision of 6 hash values.
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| @@ -1417,6 +1417,35 @@ static void deprecated_sysctl_warning(const int *name, int nlen) · 1416 unmodified lines | |||
| 1417 | return; | 1417 | return; |
| 1418 | } | 1418 | } |
| 1419 | 1419 | ||
| 1420 | #define WARN_ONCE_HASH_BITS 8 | ||
| 1421 | #define WARN_ONCE_HASH_SIZE (1<<WARN_ONCE_HASH_BITS) | ||
| 1422 | |||
| 1423 | static DECLARE_BITMAP(warn_once_bitmap, WARN_ONCE_HASH_SIZE); | ||
| 1424 | |||
| 1425 | #define FNV32_OFFSET 2166136261U | ||
| 1426 | #define FNV32_PRIME 0x01000193 | ||
| 1427 | |||
| 1428 | /* | ||
| 1429 | * Print each legacy sysctl (approximately) only once. | ||
| 1430 | * To avoid making the tables non-const use a external | ||
| 1431 | * hash-table instead. | ||
| 1432 | * Worst case hash collision: 6, but very rarely. | ||
| 1433 | * NOTE! We don't use the SMP-safe bit tests. We simply | ||
| 1434 | * don't care enough. | ||
| 1435 | */ | ||
| 1436 | static void warn_on_bintable(const int *name, int nlen) | ||
| 1437 | { | ||
| 1438 | int i; | ||
| 1439 | u32 hash = FNV32_OFFSET; | ||
| 1440 | |||
| 1441 | for (i = 0; i < nlen; i++) | ||
| 1442 | hash = (hash ^ name[i]) * FNV32_PRIME; | ||
| 1443 | hash %= WARN_ONCE_HASH_SIZE; | ||
| 1444 | if (__test_and_set_bit(hash, warn_once_bitmap)) | ||
| 1445 | return; | ||
| 1446 | deprecated_sysctl_warning(name, nlen); | ||
| 1447 | } | ||
| 1448 | |||
| 1420 | static ssize_t do_sysctl(int __user *args_name, int nlen, | 1449 | static ssize_t do_sysctl(int __user *args_name, int nlen, |
| 1421 | void __user *oldval, size_t oldlen, void __user *newval, size_t newlen) | 1450 | void __user *oldval, size_t oldlen, void __user *newval, size_t newlen) |
| 1422 | { | 1451 | { |
| @@ -1431,7 +1460,7 @@ static ssize_t do_sysctl(int __user *args_name, int nlen, · 8 unmodified lines | |||
| 1431 | if (get_user(name[i], args_name + i)) | 1460 | if (get_user(name[i], args_name + i)) |
| 1432 | return -EFAULT; | 1461 | return -EFAULT; |
| 1433 | 1462 | ||
| 1434 | deprecated_sysctl_warning(name, nlen); | 1463 | warn_on_bintable(name, nlen); |
| 1435 | 1464 | ||
| 1436 | return binary_sysctl(name, nlen, oldval, oldlen, newval, newlen); | 1465 | return binary_sysctl(name, nlen, oldval, oldlen, newval, newlen); |
| 1437 | } | 1466 | } |