[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index] Re: [Xen-devel] [Patch v3 2/2] tools/libxc: Implement writev_exact() in the same style as write_exact()
On 18/07/14 11:05, Wen Congyang wrote: > At 07/18/2014 05:53 PM, Ian Campbell Wrote: >> On Fri, 2014-07-18 at 10:20 +0100, Andrew Cooper wrote: >>> On 18/07/14 02:14, Wen Congyang wrote: >>>> At 07/16/2014 10:32 PM, Andrew Cooper Wrote: >>>>> This implementation of writev_exact() will cope with an iovcnt greater >>>>> than >>>>> IOV_MAX because glibc will actually let this work anyway, and it is very >>>>> useful not to have to work about this in the caller of writev_exact(). >>>>> The >>>>> caller is still required to ensure that the sum of iov_len's doesn't >>>>> overflow >>>>> a ssize_t. >>>>> >>>>> Signed-off-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx> >>>>> CC: Ian Campbell <Ian.Campbell@xxxxxxxxxx> >>>>> CC: Ian Jackson <Ian.Jackson@xxxxxxxxxxxxx> >>>>> >>>>> --- >>>>> v3: >>>>> * Re-add adjustment for partial writes. >>>>> * Split min/max adjustment into separate patch. >>>>> >>>>> v2: >>>>> * Remove adjustment for partial writes of a specific iov[] entry. >>>>> --- >>>>> tools/libxc/xc_private.c | 60 >>>>> ++++++++++++++++++++++++++++++++++++++++++++++ >>>>> tools/libxc/xc_private.h | 2 ++ >>>>> 2 files changed, 62 insertions(+) >>>>> >>>>> diff --git a/tools/libxc/xc_private.c b/tools/libxc/xc_private.c >>>>> index 1c214dd..0941b06 100644 >>>>> --- a/tools/libxc/xc_private.c >>>>> +++ b/tools/libxc/xc_private.c >>>>> @@ -858,6 +858,66 @@ int write_exact(int fd, const void *data, size_t >>>>> size) >>>>> return 0; >>>>> } >>>>> >>>>> +int writev_exact(int fd, const struct iovec *iov, int iovcnt) >>>>> +{ >>>>> + struct iovec *local_iov = NULL; >>>>> + int rc = 0, iov_idx = 0, saved_errno = 0; >>>>> + ssize_t len; >>>>> + >>>>> + while ( iov_idx < iovcnt ) >>>>> + { >>>>> + /* Skip over iov[] entries with 0 length. */ >>>>> + while ( iov[iov_idx].iov_len == 0 ) >>>>> + if ( ++iov_idx == iovcnt ) >>>>> + goto out; >>>> set saved_errn to 0 before goto out? >>> Good catch. >> Isn't this a success path? errno is generally undefined on success. > Yes, but we set saved_errno to 0 here: >> + saved_errno = 0; >> + >> + out: >> + free(local_iov); >> + errno = saved_errno; >> + return rc; >> +} > I think there is no need to save errno in this function, because > we return -1 when writev()/malloc() fails. > > Another problem: I am deliberately creating the same (somewhat quirky) error semantics of write_exact(), for consistency reasons. The key point is that EOF is -1 and errno of 0. >> + local_iov = malloc(iovcnt * sizeof(*iov)); >> + if ( !local_iov ) >> + { >> + saved_errno = ENOMEM; >> + goto out; >> + } >> + > rc is not set to -1 before goto out. > > Thanks > Wen Congyang Good point. ~Andrew _______________________________________________ Xen-devel mailing list Xen-devel@xxxxxxxxxxxxx http://lists.xen.org/xen-devel
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