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kernel&all: create() syscall only sends Tcreate

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In Plan9 the create syscall fallback on a open(OTRUNC) if the
path provided already exists. This is actually a common requirement
as most programs (editors, cat...) simply requires that a file is
there and is empty, and doesn't care overwriting existing contents
(note that this is particularily sensible with something like fossil).

In Jehanne the application is responsible of actually handle this
"file exists" error but libc provides ocreate() to mimic the Plan9
behaviour. Note that ocreate introduce a subtle race too: the path
is walked several times if the file exists, thus it could misbehave
on concurrent namespace changes. However I guess this is not going to
happen often enough to care now.

NOTE we will probably address this rare race too, with a more drammatic change
to syscalls: a new walk() syscall that will provide an unopen fd.
This commit is contained in:
Giacomo Tesio
2016-12-24 21:25:20 +01:00
parent 0c094289e6
commit b862596737
78 changed files with 271 additions and 289 deletions
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46
sys/include/libc.h
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@ -396,6 +396,7 @@ extern void longjmp(jmp_buf, int);
extern char* mktemp(char*);
extern double modf(double, double*);
extern void notejmp(void*, jmp_buf, int);
extern int ocreate(const char* path, unsigned int omode, unsigned int perm);
extern void perror(const char*);
extern int pipe(int pipes[2]);
extern int postnote(int, int, const char *);
@ -565,14 +566,12 @@ extern void freenetconninfo(NetConnInfo*);
/* Open modes: Popular flags among filesystems */
#define OTRUNC 0x0100 /* or'ed in (except for exec), truncate file first */
#define OEXCL 0x0200 /* or'ed in, exclusive create */
/* Access modes */
#define AEXIST OSTAT /* accessible: exists */
#define AREAD OREAD /* read access */
#define AWRITE OWRITE /* write access */
#define AEXEC OEXEC /* execute access */
#define AMASK (OSTAT|OREAD|OWRITE|OEXEC)
#define AEXIST 0 /* accessible: exists */
#define AREAD 4 /* read access */
#define AWRITE 2 /* write access */
#define AEXEC 1 /* execute access */
/* Segattch */
#define SG_RONLY 0040 /* read only */
@ -654,58 +653,23 @@ struct Waitmsg
char *msg;
} Waitmsg;
//extern void _exits(const char*) __attribute__ ((noreturn));
extern int access(const char*, int);
//extern int64_t alarm(uint64_t);
//extern int await(char*, int);
//extern int64_t awake(int64_t);
extern int awakened(int64_t);
//extern int bind(const char*, const char*, int);
extern int brk(void*);
//extern int chdir(const char*);
//extern int close(int);
//extern int create(const char*, int, uint32_t);
//extern int dup(int, int);
//extern int errstr(char*, uint32_t);
//extern int exec(const char*, char* const[]);
extern int execl(const char*, ...);
extern int forgivewkp(int64_t);
extern pid_t fork(void);
//extern pid_t rfork(int);
//extern int fauth(int, const char*);
//extern int fstat(int, uint8_t*, int);
//extern int fwstat(int, uint8_t*, int);
//extern int fversion(int, int, char*, int);
//extern int mount(int, int, const char*, int, const char*, int);
//extern int unmount(const char*, const char*);
//extern int noted(int);
//extern int notify(void(*)(void*, char*));
//extern int open(const char*, int);
//extern int fd2path(int, char*, int);
// extern int fdflush(int);
//extern int pipe(int*);
//extern int32_t pread(int, void*, int32_t, int64_t);
//extern int32_t pwrite(int, const void*, int32_t, int64_t);
//extern int32_t read(int, void*, int32_t);
extern int32_t readn(int, void*, int32_t);
//extern int remove(const char*);
extern void* sbrk(uint32_t);
extern int32_t oseek(int, int32_t, int);
//extern int64_t seek(int, int64_t, int);
extern void* segattach(int, const char*, void*, unsigned long);
extern int segdetach(void*);
extern int segfree(void*, unsigned long);
//extern int semacquire(int32_t*, int);
//extern int32_t semrelease(int32_t*, int32_t);
extern void sleep(int32_t);
extern int stat(const char*, uint8_t*, int);
//extern int tsemacquire(int32_t*, uint64_t);
extern Waitmsg* wait(void);
extern int waitpid(void);
//extern int32_t write(int, const void*, int32_t);
extern int wstat(const char*, uint8_t*, int);
//extern void* rendezvous(void*, void*);
extern Dir* dirstat(const char*);
extern Dir* dirfstat(int);