Linux errno.h和delay.h

两个小知识点总结，基于Linux3.14.52：

1、<errno.h>位于linux-3.14.52\include\uapi\asm-generic

#defineEPERM 1/* Operation not permitted */#defineENOENT 2/* No such file or directory */#defineESRCH 3/* No such process */#defineEINTR 4/* Interrupted system call */#defineEIO 5/* I/O error */#defineENXIO 6/* No such device or address */#defineE2BIG 7/* Argument list too long */#defineENOEXEC 8/* Exec format error */#defineEBADF 9/* Bad file number */#defineECHILD10/* No child processes */#defineEAGAIN11/* Try again */#defineENOMEM12/* Out of memory */#defineEACCES13/* Permission denied */#defineEFAULT14/* Bad address */#defineENOTBLK15/* Block device required */#defineEBUSY16/* Device or resource busy */#defineEEXIST17/* File exists */#defineEXDEV18/* Cross-device link */#defineENODEV19/* No such device */#defineENOTDIR20/* Not a directory */#defineEISDIR21/* Is a directory */#defineEINVAL22/* Invalid argument */#defineENFILE23/* File table overflow */#defineEMFILE24/* Too many open files */#defineENOTTY25/* Not a typewriter */#defineETXTBSY26/* Text file busy */#defineEFBIG27/* File too large */#defineENOSPC28/* No space left on device */#defineESPIPE29/* Illegal seek */#defineEROFS30/* Read-only file system */#defineEMLINK31/* Too many links */#defineEPIPE32/* Broken pipe */#defineEDOM33/* Math argument out of domain of func */#defineERANGE34/* Math result not representable */

#defineEDEADLK35/* Resource deadlock would occur */#defineENAMETOOLONG36/* File name too long */#defineENOLCK37/* No record locks available */#defineENOSYS38/* Function not implemented */#defineENOTEMPTY39/* Directory not empty */#defineELOOP40/* Too many symbolic links encountered */#defineEWOULDBLOCKEAGAIN/* Operation would block */#defineENOMSG42/* No message of desired type */#defineEIDRM43/* Identifier removed */#defineECHRNG44/* Channel number out of range */#defineEL2NSYNC45/* Level 2 not synchronized */#defineEL3HLT46/* Level 3 halted */#defineEL3RST47/* Level 3 reset */#defineELNRNG48/* Link number out of range */#defineEUNATCH49/* Protocol driver not attached */#defineENOCSI50/* No CSI structure available */#defineEL2HLT51/* Level 2 halted */#defineEBADE52/* Invalid exchange */#defineEBADR53/* Invalid request descriptor */#defineEXFULL54/* Exchange full */#defineENOANO55/* No anode */#defineEBADRQC56/* Invalid request code */#defineEBADSLT57/* Invalid slot */#defineEDEADLOCKEDEADLK#defineEBFONT59/* Bad font file format */#defineENOSTR60/* Device not a stream */#defineENODATA61/* No data available */#defineETIME62/* Timer expired */#defineENOSR63/* Out of streams resources */#defineENONET64/* Machine is not on the network */#defineENOPKG65/* Package not installed */#defineEREMOTE66/* Object is remote */#defineENOLINK67/* Link has been severed */#defineEADV68/* Advertise error */#defineESRMNT69/* Srmount error */#defineECOMM70/* Communication error on send */#defineEPROTO71/* Protocol error */#defineEMULTIHOP72/* Multihop attempted */#defineEDOTDOT73/* RFS specific error */#defineEBADMSG74/* Not a data message */#defineEOVERFLOW75/* Value too large for defined data type */#defineENOTUNIQ76/* Name not unique on network */#defineEBADFD77/* File descriptor in bad state */#defineEREMCHG78/* Remote address changed */#defineELIBACC79/* Can not access a needed shared library */#defineELIBBAD80/* Accessing a corrupted shared library */#defineELIBSCN81/* .lib section in a.out corrupted */#defineELIBMAX82/* Attempting to link in too many shared libraries */#defineELIBEXEC83/* Cannot exec a shared library directly */#defineEILSEQ84/* Illegal byte sequence */#defineERESTART85/* Interrupted system call should be restarted */#defineESTRPIPE86/* Streams pipe error */#defineEUSERS87/* Too many users */#defineENOTSOCK88/* Socket operation on non-socket */#defineEDESTADDRREQ89/* Destination address required */#defineEMSGSIZE90/* Message too long */#defineEPROTOTYPE91/* Protocol wrong type for socket */#defineENOPROTOOPT92/* Protocol not available */#defineEPROTONOSUPPORT93/* Protocol not supported */#defineESOCKTNOSUPPORT94/* Socket type not supported */#defineEOPNOTSUPP95/* Operation not supported on transport endpoint */#defineEPFNOSUPPORT96/* Protocol family not supported */#defineEAFNOSUPPORT97/* Address family not supported by protocol */#defineEADDRINUSE98/* Address already in use */#defineEADDRNOTAVAIL99/* Cannot assign requested address */#defineENETDOWN100/* Network is down */#defineENETUNREACH101/* Network is unreachable */#defineENETRESET102/* Network dropped connection because of reset */#defineECONNABORTED103/* Software caused connection abort */#defineECONNRESET104/* Connection reset by peer */#defineENOBUFS105/* No buffer space available */#defineEISCONN106/* Transport endpoint is already connected */#defineENOTCONN107/* Transport endpoint is not connected */#defineESHUTDOWN108/* Cannot send after transport endpoint shutdown */#defineETOOMANYREFS109/* Too many references: cannot splice */#defineETIMEDOUT110/* Connection timed out */#defineECONNREFUSED111/* Connection refused */#defineEHOSTDOWN112/* Host is down */#defineEHOSTUNREACH113/* No route to host */#defineEALREADY114/* Operation already in progress */#defineEINPROGRESS115/* Operation now in progress */#defineESTALE116/* Stale file handle */#defineEUCLEAN117/* Structure needs cleaning */#defineENOTNAM118/* Not a XENIX named type file */#defineENAVAIL119/* No XENIX semaphores available */#defineEISNAM120/* Is a named type file */#defineEREMOTEIO121/* Remote I/O error */#defineEDQUOT122/* Quota exceeded */#defineENOMEDIUM123/* No medium found */#defineEMEDIUMTYPE124/* Wrong medium type */#defineECANCELED125/* Operation Canceled */#defineENOKEY126/* Required key not available */#defineEKEYEXPIRED127/* Key has expired */#defineEKEYREVOKED128/* Key has been revoked */#defineEKEYREJECTED129/* Key was rejected by service *//* for robust mutexes */#defineEOWNERDEAD130/* Owner died */#defineENOTRECOVERABLE131/* State not recoverable */#define ERFKILL132/* Operation not possible due to RF-kill */#define EHWPOISON133/* Memory page has hardware error */

2、delay.h位于inux-3.14.52\include\linux，其中包括mdelay()、udelay()和ndelay()三个函数，分别代表ms、us、ns级别的延时。但是，ndelay()是假的！！！

Linux只能提供微秒级别的延时，所谓纳秒，其实也是利用比它大一级的微秒延时做的。所以ndelay(1)和ndelay(999)是一样的，都将转换为udelay(1)

#ifndef mdelay#define mdelay(n)    (/(__builtin_constant_p(n) && (n)<=MAX_UDELAY_MS) ? udelay((n)*1000) : /({unsigned long __ms=(n); while (__ms--) udelay(1000);}))#endif#ifndef ndelay#define ndelay(x) udelay(((x)+999)/1000)#endif