diff options
Diffstat (limited to 'lib/libstand/lseek.c')
| -rw-r--r-- | lib/libstand/lseek.c | 31 |
1 files changed, 31 insertions, 0 deletions
diff --git a/lib/libstand/lseek.c b/lib/libstand/lseek.c index 91f8612..f945460 100644 --- a/lib/libstand/lseek.c +++ b/lib/libstand/lseek.c @@ -70,6 +70,7 @@ off_t lseek(int fd, off_t offset, int where) { + off_t bufpos, filepos, target; struct open_file *f = &files[fd]; if ((unsigned)fd >= SOPEN_MAX || f->f_flags == 0) { @@ -97,6 +98,36 @@ lseek(int fd, off_t offset, int where) } /* + * If there is some unconsumed data in the readahead buffer and it + * contains the desired offset, simply adjust the buffer offset and + * length. We don't bother with SEEK_END here, since the code to + * handle it would fail in the same cases where the non-readahead + * code fails (namely, for streams which cannot seek backward and whose + * size isn't known in advance). + */ + if (f->f_ralen != 0 && where != SEEK_END) { + if ((filepos = (f->f_ops->fo_seek)(f, (off_t)0, SEEK_CUR)) == -1) + return (-1); + bufpos = filepos - f->f_ralen; + switch (where) { + case SEEK_SET: + target = offset; + break; + case SEEK_CUR: + target = bufpos + offset; + break; + default: + errno = EINVAL; + return (-1); + } + if (bufpos <= target && target < filepos) { + f->f_raoffset += target - bufpos; + f->f_ralen -= target - bufpos; + return (target); + } + } + + /* * If this is a relative seek, we need to correct the offset for * bytes that we have already read but the caller doesn't know * about. |
