66 lines
2.0 KiB
C
66 lines
2.0 KiB
C
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#include <fcntl.h>
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#include <poll.h>
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#include <stdio.h>
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#include <sys/stat.h>
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#include <sys/types.h>
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#include <stdlib.h>
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#include <time.h>
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#include <unistd.h>
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#include <dlfcn.h>
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enum { BufSize = 64*1024 };
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typedef int (*open_t)( const char*, int, ... );
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typedef void (*exit_t)( int );
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typedef int (*poll_t)( struct pollfd*, nfds_t, int timeout );
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typedef int (*nanosleep_t)( const struct timespec*, struct timespec* );
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typedef ssize_t (*read_t)( int, void*, size_t );
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typedef ssize_t (*write_t)( int, const void*, size_t );
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void _start()
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{
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void* libc = dlopen( "libc.so", RTLD_LAZY );
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open_t sym_open = dlsym( libc, "open" );
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exit_t sym_exit = dlsym( libc, "exit" );
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poll_t sym_poll = dlsym( libc, "poll" );
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nanosleep_t sym_nanosleep = dlsym( libc, "nanosleep" );
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read_t sym_read = dlsym( libc, "read" );
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write_t sym_write = dlsym( libc, "write" );
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char buf[BufSize];
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int kernelFd = sym_open( "/sys/kernel/debug/tracing/trace_pipe", O_RDONLY );
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if( kernelFd < 0 ) sym_exit( 0 );
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struct pollfd pfd_in;
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pfd_in.fd = kernelFd;
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pfd_in.events = POLLIN | POLLERR;
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struct pollfd pfd_out;
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pfd_out.fd = STDOUT_FILENO;
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pfd_out.events = POLLERR;
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struct timespec sleepTime;
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sleepTime.tv_sec = 0;
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sleepTime.tv_nsec = 1000 * 1000 * 10;
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// While the pipe is open (no POLLERR on the output fd)
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while( sym_poll( &pfd_out, 1, 0) <= 0 )
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{
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// If there is neither data (POLLIN) nor an error (POLLERR) on
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// the read fd, sleep. This implements a blocking read without relying
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// on the Linux kernel's implementation of blocking reads which causes
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// a large number of context switches.
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if( sym_poll( &pfd_in, 1, 0 ) <= 0 ) {
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sym_nanosleep( &sleepTime, NULL );
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continue; // go back to the while condition polling the output fd
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}
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const ssize_t rd = sym_read( kernelFd, buf, BufSize );
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if( rd <= 0 ) break;
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sym_write( STDOUT_FILENO, buf, rd );
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}
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sym_exit( 0 );
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}
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