On Wed, Jun 22, 2016 at 04:43:18PM +0200, Michal Privoznik wrote:
This function takes a FD and determines whether the current position is in data section or in a hole. In addition to that, it also determines how much bytes are there remaining till the current section ends.
Signed-off-by: Michal Privoznik <mprivozn@redhat.com> --- src/libvirt_private.syms | 1 + src/util/virfile.c | 70 ++++++++++++++++++++++++++++++++++++++++++++++++ src/util/virfile.h | 4 +++ 3 files changed, 75 insertions(+)
diff --git a/src/libvirt_private.syms b/src/libvirt_private.syms index 501c23e..f476eae 100644 --- a/src/libvirt_private.syms +++ b/src/libvirt_private.syms @@ -1513,6 +1513,7 @@ virFileGetHugepageSize; virFileGetMountReverseSubtree; virFileGetMountSubtree; virFileHasSuffix; +virFileInData; virFileIsAbsPath; virFileIsDir; virFileIsExecutable; diff --git a/src/util/virfile.c b/src/util/virfile.c index f47bf39..05b709a 100644 --- a/src/util/virfile.c +++ b/src/util/virfile.c @@ -3443,3 +3443,73 @@ int virFileIsSharedFS(const char *path) VIR_FILE_SHFS_SMB | VIR_FILE_SHFS_CIFS); } + + +int virFileInData(int fd, + int *inData, + unsigned long long *length) +{ + int ret = -1; + off_t cur, data, hole; + + /* Get current position */ + cur = lseek(fd, 0, SEEK_CUR); + if (cur == (off_t) -1) { + virReportSystemError(errno, "%s", + _("Unable to get current position in file")); + goto cleanup; + } + + /* Now try to get data and hole offsets */ + data = lseek(fd, cur, SEEK_DATA); + + /* There are four options: + * 1) data == cur; @cur is in data + * 2) data > cur; @cur is in a hole, next data at @data + * 3) data < 0, errno = ENXIO; either @cur is in trailing hole, or @cur is beyond EOF. + * 4) data < 0, errno != ENXIO; we learned nothing + */ + + if (data == (off_t) -1) { + /* cases 3 and 4 */ + if (errno != ENXIO) { + virReportSystemError(errno, "%s", + _("Unable to seek to data")); + goto cleanup; + } + *inData = 0; + *length = 0; + } else if (data > cur) { + /* case 2 */ + *inData = 0; + *length = data - cur; + } else { + /* case 1 */ + *inData = 1; + + /* We don't know where does the next hole start. Let's + * find out. Here we get the same 4 possibilities as + * described above.*/ + hole = lseek(fd, data, SEEK_HOLE); + if (hole == (off_t) -1 || hole == data) { + /* cases 1, 3 and 4 */ + /* Wait a second. The reason why we are here is + * because we are in data. But at the same time we + * are in a trailing hole? Wut!? Do the best what we + * can do here. */ + virReportSystemError(errno, "%s", + _("unable to seek to hole")); + goto cleanup; + } else { + /* case 2 */ + *length = (hole - data); + } + } + + ret = 0; + cleanup: + /* At any rate, reposition back to where we started. */ + if (cur != (off_t) -1) + ignore_value(lseek(fd, cur, SEEK_SET));
Is it really safe to ignore the value here ? IIUC, callers of this function would be justified in thinking it would *not* have a side effect on file position. IOW, I think we'd probably want to treat this error as fatal too. I think it'd be desirable to have a unit test written explicitly for this function, since there's a few fun edge cases to worry about here. Regards, Daniel -- |: http://berrange.com -o- http://www.flickr.com/photos/dberrange/ :| |: http://libvirt.org -o- http://virt-manager.org :| |: http://autobuild.org -o- http://search.cpan.org/~danberr/ :| |: http://entangle-photo.org -o- http://live.gnome.org/gtk-vnc :|