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e56fc58bf3
dmesg only flushes when it encounter a newline. Without a newline, the line is held in memory pending another printk. In this particular example (example_atomic.c), the last pr_info in atomic_bitwise() prints when another printk happens (either by another module, or __exit for this module. This can be confusing to new learner. This patch adds a newline to the last pr_info forcing dmesg to print to the screen when the module is loaded.
76 lines
1.9 KiB
C
76 lines
1.9 KiB
C
/*
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* example_atomic.c
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*/
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#include <linux/atomic.h>
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#include <linux/bitops.h>
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#include <linux/module.h>
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#include <linux/printk.h>
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#define BYTE_TO_BINARY_PATTERN "%c%c%c%c%c%c%c%c"
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#define BYTE_TO_BINARY(byte) \
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((byte & 0x80) ? '1' : '0'), ((byte & 0x40) ? '1' : '0'), \
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((byte & 0x20) ? '1' : '0'), ((byte & 0x10) ? '1' : '0'), \
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((byte & 0x08) ? '1' : '0'), ((byte & 0x04) ? '1' : '0'), \
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((byte & 0x02) ? '1' : '0'), ((byte & 0x01) ? '1' : '0')
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static void atomic_add_subtract(void)
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{
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atomic_t debbie;
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atomic_t chris = ATOMIC_INIT(50);
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atomic_set(&debbie, 45);
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/* subtract one */
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atomic_dec(&debbie);
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atomic_add(7, &debbie);
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/* add one */
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atomic_inc(&debbie);
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pr_info("chris: %d, debbie: %d\n", atomic_read(&chris),
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atomic_read(&debbie));
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}
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static void atomic_bitwise(void)
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{
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unsigned long word = 0;
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pr_info("Bits 0: " BYTE_TO_BINARY_PATTERN, BYTE_TO_BINARY(word));
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set_bit(3, &word);
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set_bit(5, &word);
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pr_info("Bits 1: " BYTE_TO_BINARY_PATTERN, BYTE_TO_BINARY(word));
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clear_bit(5, &word);
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pr_info("Bits 2: " BYTE_TO_BINARY_PATTERN, BYTE_TO_BINARY(word));
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change_bit(3, &word);
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pr_info("Bits 3: " BYTE_TO_BINARY_PATTERN, BYTE_TO_BINARY(word));
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if (test_and_set_bit(3, &word))
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pr_info("wrong\n");
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pr_info("Bits 4: " BYTE_TO_BINARY_PATTERN, BYTE_TO_BINARY(word));
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word = 255;
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pr_info("Bits 5: " BYTE_TO_BINARY_PATTERN "\n", BYTE_TO_BINARY(word));
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}
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static int __init example_atomic_init(void)
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{
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pr_info("example_atomic started\n");
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atomic_add_subtract();
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atomic_bitwise();
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return 0;
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}
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static void __exit example_atomic_exit(void)
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{
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pr_info("example_atomic exit\n");
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}
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module_init(example_atomic_init);
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module_exit(example_atomic_exit);
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MODULE_DESCRIPTION("Atomic operations example");
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MODULE_LICENSE("GPL");
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