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Mon, 16 May 2022 07:19:09 +0000 (UTC) Received: from blackfin.pond.sub.org (unknown [10.36.112.4]) by smtp.corp.redhat.com (Postfix) with ESMTPS id B54A454ED1F; Mon, 16 May 2022 07:19:08 +0000 (UTC) Received: by blackfin.pond.sub.org (Postfix, from userid 1000) id 80BC021E690D; Mon, 16 May 2022 09:19:07 +0200 (CEST) From: Markus Armbruster To: marcandre.lureau@redhat.com Cc: qemu-devel@nongnu.org, Konstantin Kostiuk , Michael Roth Subject: Re: [PATCH v3 04/15] qga: flatten safe_open_or_create() References: <20220513180821.905149-1-marcandre.lureau@redhat.com> <20220513180821.905149-5-marcandre.lureau@redhat.com> Date: Mon, 16 May 2022 09:19:07 +0200 In-Reply-To: <20220513180821.905149-5-marcandre.lureau@redhat.com> (marcandre lureau's message of "Fri, 13 May 2022 20:08:10 +0200") Message-ID: <87k0ameyhg.fsf@pond.sub.org> User-Agent: Gnus/5.13 (Gnus v5.13) Emacs/27.2 (gnu/linux) MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: quoted-printable X-Scanned-By: MIMEDefang 2.85 on 10.11.54.9 Received-SPF: pass client-ip=170.10.129.124; envelope-from=armbru@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-Spam_score_int: -28 X-Spam_score: -2.9 X-Spam_bar: -- X-Spam_report: (-2.9 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.082, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, RCVD_IN_DNSWL_LOW=-0.7, SPF_HELO_NONE=0.001, SPF_PASS=-0.001, T_SCC_BODY_TEXT_LINE=-0.01 autolearn=ham autolearn_force=no X-Spam_action: no action X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" marcandre.lureau@redhat.com writes: > From: Marc-Andr=C3=A9 Lureau > > There is a bit too much nesting in the function, this can be simplified > a bit to improve readability. > > This also helps with the following error handling changes. > > Signed-off-by: Marc-Andr=C3=A9 Lureau > --- > qga/commands-posix.c | 122 ++++++++++++++++++++++--------------------- > 1 file changed, 62 insertions(+), 60 deletions(-) > > diff --git a/qga/commands-posix.c b/qga/commands-posix.c > index 69f209af87..15eb7cb77d 100644 > --- a/qga/commands-posix.c > +++ b/qga/commands-posix.c > @@ -339,73 +339,75 @@ find_open_flag(const char *mode_str, Error **errp) > static FILE * > safe_open_or_create(const char *path, const char *mode, Error **errp) > { > - Error *local_err =3D NULL; > int oflag; > + int fd =3D -1; > + FILE *f =3D NULL; > + > + oflag =3D find_open_flag(mode, errp); > + if (oflag < 0) { > + goto end; > + } > + > + /* If the caller wants / allows creation of a new file, we implement= it > + * with a two step process: open() + (open() / fchmod()). > + * > + * First we insist on creating the file exclusively as a new file. If > + * that succeeds, we're free to set any file-mode bits on it. (The > + * motivation is that we want to set those file-mode bits independen= tly > + * of the current umask.) > + * > + * If the exclusive creation fails because the file already exists > + * (EEXIST is not possible for any other reason), we just attempt to > + * open the file, but in this case we won't be allowed to change the > + * file-mode bits on the preexistent file. > + * > + * The pathname should never disappear between the two open()s in > + * practice. If it happens, then someone very likely tried to race u= s. > + * In this case just go ahead and report the ENOENT from the second > + * open() to the caller. > + * > + * If the caller wants to open a preexistent file, then the first > + * open() is decisive and its third argument is ignored, and the sec= ond > + * open() and the fchmod() are never called. > + */ > + fd =3D open(path, oflag | ((oflag & O_CREAT) ? O_EXCL : 0), 0); > + if (fd =3D=3D -1 && errno =3D=3D EEXIST) { > + oflag &=3D ~(unsigned)O_CREAT; > + fd =3D open(path, oflag); > + } > + if (fd =3D=3D -1) { > + error_setg_errno(errp, errno, > + "failed to open file '%s' " > + "(mode: '%s')", No need to split this string. > + path, mode); > + goto end; > + } >=20=20 > - oflag =3D find_open_flag(mode, &local_err); > - if (local_err =3D=3D NULL) { > - int fd; > - > - /* If the caller wants / allows creation of a new file, we imple= ment it > - * with a two step process: open() + (open() / fchmod()). > - * > - * First we insist on creating the file exclusively as a new fil= e. If > - * that succeeds, we're free to set any file-mode bits on it. (T= he > - * motivation is that we want to set those file-mode bits indepe= ndently > - * of the current umask.) > - * > - * If the exclusive creation fails because the file already exis= ts > - * (EEXIST is not possible for any other reason), we just attemp= t to > - * open the file, but in this case we won't be allowed to change= the > - * file-mode bits on the preexistent file. > - * > - * The pathname should never disappear between the two open()s in > - * practice. If it happens, then someone very likely tried to ra= ce us. > - * In this case just go ahead and report the ENOENT from the sec= ond > - * open() to the caller. > - * > - * If the caller wants to open a preexistent file, then the first > - * open() is decisive and its third argument is ignored, and the= second > - * open() and the fchmod() are never called. > - */ > - fd =3D open(path, oflag | ((oflag & O_CREAT) ? O_EXCL : 0), 0); > - if (fd =3D=3D -1 && errno =3D=3D EEXIST) { > - oflag &=3D ~(unsigned)O_CREAT; > - fd =3D open(path, oflag); > - } > + qemu_set_cloexec(fd); >=20=20 > - if (fd =3D=3D -1) { > - error_setg_errno(&local_err, errno, "failed to open file '%s= ' " > - "(mode: '%s')", path, mode); > - } else { > - qemu_set_cloexec(fd); > + if ((oflag & O_CREAT) && fchmod(fd, DEFAULT_NEW_FILE_MODE) =3D=3D -1= ) { > + error_setg_errno(errp, errno, > + "failed to set permission 0%03o on new file '%s= ' (mode: '%s')", But I'd split this one. > + (unsigned)DEFAULT_NEW_FILE_MODE, path, mode); > + goto end; > + } >=20=20 > - if ((oflag & O_CREAT) && fchmod(fd, DEFAULT_NEW_FILE_MODE) = =3D=3D -1) { > - error_setg_errno(&local_err, errno, "failed to set permi= ssion " > - "0%03o on new file '%s' (mode: '%s')", > - (unsigned)DEFAULT_NEW_FILE_MODE, path, = mode); > - } else { > - FILE *f; > - > - f =3D fdopen(fd, mode); > - if (f =3D=3D NULL) { > - error_setg_errno(&local_err, errno, "failed to assoc= iate " > - "stdio stream with file descriptor = %d, " > - "file '%s' (mode: '%s')", fd, path,= mode); > - } else { > - return f; > - } > - } > + f =3D fdopen(fd, mode); > + if (f =3D=3D NULL) { > + error_setg_errno(errp, errno, > + "failed to associate stdio stream with file des= criptor %d, " > + "file '%s' (mode: '%s')", And I'd split this one like "failed to associate stdio stream with" " file descriptor %d, file '%s' (mode: '%s')", > + fd, path, mode); > + } >=20=20 > - close(fd); > - if (oflag & O_CREAT) { > - unlink(path); > - } > +end: Cases here: 1. find_open_flag() or open() failed (first two goto): @fd is -1, @f is NULL 2. open() succeeded, fchmod() failed (third goto), or open() succeeded, fdopen() failed (fall through): @fd is open, @f is NULL 3. open() and fdopen() succeeded: @fd and @f are open > + if (f =3D=3D NULL && fd !=3D -1) { This is case 2. > + close(fd); > + if (oflag & O_CREAT) { > + unlink(path); > } > } > - > - error_propagate(errp, local_err); > - return NULL; > + return f; Works. Case 1 could return NULL instead of goto end. The condition for close(fd) then becomes if (!f). Feels simpler to me, but I guess it's a matter of taste. > } >=20=20 > int64_t qmp_guest_file_open(const char *path, bool has_mode, const char = *mode, None of the above is serious, so Reviewed-by: Markus Armbruster