diff options
Diffstat (limited to 'src/shared')
| -rw-r--r-- | src/shared/missing.h | 10 | ||||
| -rw-r--r-- | src/shared/util.c | 48 |
2 files changed, 54 insertions, 4 deletions
diff --git a/src/shared/missing.h b/src/shared/missing.h index 5cf179ef00..cdc38b2dd8 100644 --- a/src/shared/missing.h +++ b/src/shared/missing.h @@ -711,3 +711,13 @@ static inline int renameat2(int oldfd, const char *oldname, int newfd, const cha #ifndef RENAME_NOREPLACE #define RENAME_NOREPLACE (1 << 0) #endif + +#if !HAVE_DECL_KCMP +static inline int kcmp(pid_t pid1, pid_t pid2, int type, unsigned long idx1, unsigned long idx2) { + return syscall(__NR_kcmp, pid1, pid2, type, idx1, idx2); +} +#endif + +#ifndef KCMP_FILE +#define KCMP_FILE 0 +#endif diff --git a/src/shared/util.c b/src/shared/util.c index 409ccc7eed..64059065d8 100644 --- a/src/shared/util.c +++ b/src/shared/util.c @@ -7678,13 +7678,35 @@ int fd_setcrtime(int fd, usec_t usec) { int same_fd(int a, int b) { struct stat sta, stb; + pid_t pid; + int r, fa, fb; assert(a >= 0); assert(b >= 0); + /* Compares two file descriptors. Note that semantics are + * quite different depending on whether we have kcmp() or we + * don't. If we have kcmp() this will only return true for + * dup()ed file descriptors, but not otherwise. If we don't + * have kcmp() this will also return true for two fds of the same + * file, created by separate open() calls. Since we use this + * call mostly for filtering out duplicates in the fd store + * this difference hopefully doesn't matter too much. */ + if (a == b) return true; + /* Try to use kcmp() if we have it. */ + pid = getpid(); + r = kcmp(pid, pid, KCMP_FILE, a, b); + if (r == 0) + return true; + if (r > 0) + return false; + if (errno != ENOSYS) + return -errno; + + /* We don't have kcmp(), use fstat() instead. */ if (fstat(a, &sta) < 0) return -errno; @@ -7694,9 +7716,27 @@ int same_fd(int a, int b) { if ((sta.st_mode & S_IFMT) != (stb.st_mode & S_IFMT)) return false; - if (S_ISREG(sta.st_mode) || S_ISDIR(sta.st_mode) || S_ISFIFO(sta.st_mode) || S_ISSOCK(sta.st_mode) || S_ISLNK(sta.st_mode)) - return (sta.st_dev == stb.st_dev) && (sta.st_ino == stb.st_ino); + /* We consider all device fds different, since two device fds + * might refer to quite different device contexts even though + * they share the same inode and backing dev_t. */ - /* We consider all device fds different... */ - return false; + if (S_ISCHR(sta.st_mode) || S_ISBLK(sta.st_mode)) + return false; + + if (sta.st_dev != stb.st_dev || sta.st_ino != stb.st_ino) + return false; + + /* The fds refer to the same inode on disk, let's also check + * if they have the same fd flags. This is useful to + * distuingish the read and write side of a pipe created with + * pipe(). */ + fa = fcntl(a, F_GETFL); + if (fa < 0) + return -errno; + + fb = fcntl(b, F_GETFL); + if (fb < 0) + return -errno; + + return fa == fb; } |