[libvirt] [PATCH 2/2] virCommand: document behavior on no output

Option 2. Which one should I go with? By the way, my pending patch for converting openvz to use virCommand instead of popen is impacted (it has a potential null dereference if we go with option 1). * docs/internals/command.html.in: Update documentation. * src/util/command.c (virCommandSetOutputBuffer) (virCommandSetErrorBuffer, virCommandProcessIO) Guarantee empty string on no output. --- docs/internals/command.html.in | 8 +++++--- src/util/command.c | 14 ++++++++++++++ 2 files changed, 19 insertions(+), 3 deletions(-) diff --git a/docs/internals/command.html.in b/docs/internals/command.html.in index ea9ec64..d2fb133 100644 --- a/docs/internals/command.html.in +++ b/docs/internals/command.html.in @@ -348,9 +348,11 @@ </pre> <p> - Once the command has finished executing, these buffers - will contain the output, or be NULL if there was no output. It - is the callers responsibility to free these buffers. + Once the command has finished executing, these buffers will + contain the output. If there was no output but virCommandRun + was successful, then they will be an empty string; if there was + an error, then they might still be NULL. It is the callers + responsibility to free these buffers. </p> <h3><a name="directory">Setting working directory</a></h3> diff --git a/src/util/command.c b/src/util/command.c index 1923799..4fb5048 100644 --- a/src/util/command.c +++ b/src/util/command.c @@ -860,6 +860,20 @@ virCommandProcessIO(virCommandPtr cmd) } } + /* If there was no output, the populate with the empty string. */ + if (cmd->outbuf && !*cmd->outbuf) { + if ((*cmd->outbuf = strdup("")) == NULL) { + virReportOOMError(); + return -1; + } + } + if (cmd->errbuf && !*cmd->errbuf) { + if ((*cmd->errbuf = strdup("")) == NULL) { + virReportOOMError(); + return -1; + } + } + return 0; } -- 1.7.3.2